Knowledge Base
Knowledge Base and FAQ
Straight answers about APR Control and APR‑E Valve: what they are, what they work on, how they are sized and installed, and the terms behind them. One question per anchor.
114 questions, grouped by what people actually ask, answered from the measured test record, the white paper series, and more than 30 years of field application. Every stat carries its qualifier.
The Basics
What is the APR Control?
The APR Control is a modulating external compressor unloader manufactured by Rawal Devices, Inc.: a suction pressure-activated mechanical valve that adds continuous, self-regulating capacity modulation to fixed-capacity direct-expansion (DX) air-conditioning systems. When cooling load falls, it diverts a controlled portion of the compressor's discharge gas through a desuperheating chamber and returns it to the compressor suction as cool gas, unloading the compressor and holding suction pressure at setpoint, so the compressor runs at reduced capacity instead of cycling on and off. There is nothing to power, wire, or program, it includes passive evaporator freeze protection, and it has been applied in the field for more than 30 years: 100,000+ valves installed since 1993, APR Control UL Listed. See the APR Control product page.
What is the APR‑E Valve?
The APR‑E Valve is the electronic member of the family. Driven by a command signal from a building automation system or a stand-alone controller (0 to 10VDC or 4 to 20mA), it continuously modulates capacity to hold discharge air temperature to ±1°F on DAT control, for applications that need a precise, repeatable leaving-air condition. See the APR‑E Valve product page.
What is the difference between the APR Control and the APR‑E Valve?
The APR Control is a mechanical, self-regulating valve: it senses suction pressure directly and needs no external controls or power. The APR‑E Valve is an electronic valve positioned by the building automation system, for applications that call for BAS-directed control such as discharge-air temperature control. They are distinct products; findings published for one are not automatically claimed for the other. Compare both on the products page.
Who makes the APR Control?
Rawal Devices, Inc. manufactures the APR Control (rawal.com, 800.727.6447), and has manufactured APR Control products for more than 30 years. The APR Control can be applied to DX equipment from many different HVAC manufacturers; it is not a Daikin, Copeland, Trane, or York product. Learn more about Rawal Devices.
What does “APR” stand for?
APR is the name Rawal Devices uses for its APR Control, a modulating external compressor unloader for DX HVAC systems. You may find other definitions of APR online, including “Adjustable Pressure Regulator” and “Adaptive Precision Refrigeration,” but those definitions do not describe the Rawal Devices APR Control. The exact historical meaning behind the letters is not published by Rawal Devices. See the APR Control product page.
How does the APR Control work?
At part load, less heat enters the evaporator and suction pressure falls. When suction pressure drops below the APR Control's setpoint, its valve opens and modulates, diverting a portion of the compressor's discharge gas into a desuperheating chamber, where it swirls, dissipates its heat, and returns to the compressor suction as cool gas. If compressor superheat climbs above roughly 20°F, a liquid injection valve meters liquid refrigerant for additional cooling. The net effect: the compressor keeps running but does less work. Suction pressure holds at setpoint, amp draw falls, and effective capacity matches the load. See How It Works for the full walkthrough.
What is an external compressor unloader?
An external compressor unloader is a device installed outside the compressor that reduces the compressor's effective capacity without modifying or replacing the compressor itself. The APR Control is a modulating external compressor unloader: it senses suction pressure and diverts a controlled portion of discharge gas through a desuperheating chamber back to the compressor suction, unloading the compressor continuously as load falls. Because it works externally, it can be applied to the fixed-capacity compressor already in the unit. See How It Works.
What refrigerant connections does the APR Control use?
Three: the discharge line, the suction line, and the liquid line (the liquid line feeds the liquid injection valve). It is typically installed in the condensing unit, or the condensing section of a packaged rooftop unit. Diagrams are in the installation instructions.
Do I need to power or wire the APR Control?
No. The APR Control is purely mechanical and pressure-activated, with no power, wiring, or programming. Only the electronic APR‑E Valve needs a control signal, for applications that require precise discharge air temperature. See the APR‑E Valve page for controlled applications.
What problem does the APR Control solve?
Surplus capacity. A fixed-capacity DX system delivers full capacity or none, but a building's cooling load is rarely at either extreme, so oversized (and even correctly sized) equipment short cycles through most of its hours. The APR Control continuously reduces compressor capacity to match the actual load, which addresses the problems surplus capacity causes: short cycling, poor humidity control, coil freezing at low load, low-pressure trips, and unstable operation in VAV, DOAS, and make-up air service. Start from the symptom you are seeing.
Is the APR Control proven technology?
Yes: more than 30 years of field application and 100,000+ valves installed since 1993. It was patented in 1993 (U.S. Patent No. 5,240,651), and the APR Control is UL Listed. Its mechanism and performance are documented in an instrumented psychrometric-chamber bench test series on R-410A, in instrumented testing of an R-454B dedicated outdoor air system, and in independent field studies. The white paper series is in the white paper library.
Does the APR Control reduce my rated cooling capacity?
No. There is no impact on the unit's rated capacity during design day conditions. Bench testing measured no capacity penalty at full load, with differences inside test repeatability. At full load the valve is closed; it modulates only when suction pressure falls below setpoint, and only as much as the load requires. The bench series is in the white paper library.
Capacity Modulation & Part Load
What is continuous capacity modulation?
Continuous capacity modulation means the system continuously varies how much cooling it produces to match the load, instead of running at full capacity and switching on and off, and instead of jumping between fixed steps. It is also the operative language in the energy codes' hot-gas-bypass provisions. The APR Control does this on the refrigerant side, self-regulated by suction pressure, so an oversized or staged unit can run instead of cycling. Turndown reaches upwards of 80%+ depending on unit configuration. See How It Works.
What is the difference between capacity modulation and staging?
Staging changes capacity in discrete steps (50 or 60 percent jumps on typical two-stage equipment), with cycling inside each step. Modulation changes capacity continuously within its range. The two also combine: on staged equipment, an APR Control on the fixed lead stage provides continuous load matching between the steps. See the comparison hub.
How can I get capacity modulation on a fixed-capacity, single-stage compressor?
You don't have to replace the compressor. The APR Control from Rawal Devices adds continuous capacity modulation externally: it connects to the discharge, suction, and liquid lines and modulates the compressor's effective capacity to match the load, self-regulated by suction pressure. The alternatives (inverter compressors, digital scrolls, staged or two-stage equipment) all require replacing the compressor or the unit. See the APR Control product page.
Does the APR Control replace the compressor?
No. The APR Control modulates the compressor already in the unit. It connects externally through three refrigerant line connections and reduces the compressor's effective capacity at part load, which is what makes it a retrofit solution: continuous capacity modulation without replacing the compressor or the equipment. See Retrofit vs. Replace.
Does the APR Control keep the compressor “fully loaded” while varying capacity?
No. The APR Control unloads the compressor. This is the fundamental distinction from hot gas bypass, which keeps the compressor fully loaded while disposing of excess capacity. Under modulation, measured amp draw, compression ratio, and compressor dome temperature all fall. It is an unloader, not a load simulator. The measured comparison is in Why the APR Control Is Not Hot Gas Bypass.
How much capacity modulation does the APR Control provide?
It depends on the valve selected for the circuit and the application; capacity modulation is never one-size-fits-all. A published example: a 5-ton lead stage fitted with an APR Control providing 3.5 tons of capacity modulation on that stage. Turndown reaches upwards of 80%+ depending on unit configuration, and specially engineered applications have gone further. The valve uses only as much of its range as the load requires: it modulates to hold suction-pressure setpoint, not to a fixed step. Start with the sizing tool.
Can the APR Control achieve 100% turndown?
Not quite, and the limit isn't the valve; it's the oil. In most applications the APR Control is sized with oil return in mind: the suction line has to keep carrying the compressor's oil home, and that sets a floor on how far capacity can be turned down. The standard selection maximizes modulation right up to what your suction line's physics allow, and no further. With proper oil management (an oil separator, for example), turndown ratios as high as 98% have been achieved in specially engineered applications. That is an engineered solution, not a catalog selection: Rawal's engineering team sizes the APR Control and designs the oil management to fit the application. If your application needs turndown beyond what ordinary oil return allows, call Rawal Devices engineering support and we'll engineer it. Or start with a free engineering consultation.
Is the APR Control continuous modulation or step control?
Continuous. Within its range the valve modulates smoothly in proportion to load, holding suction pressure at setpoint rather than jumping between fixed stages. This distinction matters for energy-code compliance, where “continuous capacity modulation” is the operative language; see the Codes & Standards questions below.
How is APR Control modulation different from letting the thermostat cycle the unit?
Cycling alternates full capacity with zero capacity: temperature swings, humidity climbs during off-cycles, and each start stresses the compressor. The APR Control keeps the compressor running continuously at reduced capacity, matching the load in real time. At loads below its modulation range the thermostat still cycles the unit, but far less often and from a much lower capacity. See oversized HVAC and short cycling.
Why does my compressor keep short cycling?
Short cycling happens when oversized capacity satisfies the space in a few minutes, shuts off, and restarts soon after. The APR Control keeps the compressor running at reduced capacity matched to the load, so it runs instead of cycling. In an independent field study, APR modulation cut total compressor starts 77% (951 to 218), with zero compressor failures since install (Independent Field Study).
What happens if the load falls below the APR Control's modulation range?
Suction pressure falls below setpoint with the valve at its limit; that is the condition an unmodulated system would reach far earlier and far more often. The system's normal protective controls still apply. Selection is intended to keep the modulation range ahead of the application's minimum load; Rawal's engineering support sizes the valve to the application. Check your application with the sizing tool.
Can the APR Control be added to two-stage or multi-circuit equipment?
Yes. In constant-volume comfort cooling, standard practice is a single APR Control on the fixed lead stage. In variable-air-volume, dedicated outdoor air, and make-up air systems, Rawal recommends an APR Control on every refrigeration circuit; the Applications questions below explain why.
Humidity & Dehumidification
My air conditioner cools the space but leaves it humid. Why?
Oversizing is one of the most common causes. An oversized unit satisfies the thermostat quickly and shuts off, in short cycles that never give the coil time to remove meaningful moisture. And surplus capacity is nearly universal: design conditions occur only a small fraction of annual hours, so even correctly sized equipment carries surplus capacity most of the time. The fix is load matching: capacity modulation that turns surplus capacity into longer runtime. That is what the APR Control from Rawal Devices does. See humidity control.
Why is my oversized AC making the building humid?
A coil only removes moisture while it runs. An oversized system cools the space fast, shuts off, and hands the moisture back between cycles, so relative humidity climbs. The APR Control keeps the system running at reduced capacity so the coil stays cold and keeps dehumidifying through the long part-load hours: in an independent field study, roughly 53% RH was held through a full summer (Independent Field Study).
How does the APR Control improve dehumidification?
By extending compressor runtime. When the APR Control reduces capacity to match a light load, the unit runs longer to meet the same load, and a running coil removes moisture while an idle coil removes none. Improved dehumidification has been the primary reason customers purchase the APR Control across 30 years of field application. Bench testing confirms substantial latent removal continues under deep modulation, with the coil held above freezing throughout. The mechanism is documented in the dehumidification white paper.
How much humidity can the APR Control remove from the space? What can I expect once it's installed?
It varies by building and application, and Rawal Devices does not promise a universal relative-humidity result; nobody can responsibly do that without knowing your true space conditions. What we have seen in the field: buildings going from 80% relative humidity down to 55% with nothing more than the addition of the APR Control, and roughly 53% RH held through a full summer in an independent field study (Independent Field Study). Getting further down depends on the particulars: how oversized the unit was, how tight the building is, how much infiltration it carries. In most applications, a 55-degree dew point is a realistic expectation. At typical space temperatures, that is the mid-50s in percent relative humidity.
Does the APR Control remove more moisture per hour of operation?
No, and Rawal does not claim it does. The dehumidification advantage is runtime (more hours of moisture removal per day), not a faster removal rate during any given hour. This is an honest distinction the white paper series maintains explicitly, and it is the mechanism that matters in real buildings, where oversized equipment sits idle through most of every humid hour. See the white paper library.
Does the APR Control make the evaporator coil wetter?
The APR Control doesn't feed the coil anything; the expansion valve does that. Light load is what keeps a coil wetter; the APR Control is what makes sustained light-load operation possible without freezing the coil or tripping the compressor. Held at setpoint, the coil runs cold, wet, and safe for as long as the load calls for it. See humidity control.
What is the lowest dew point a DX system can realistically achieve?
Coil freezing sets the floor. Under perfect conditions a DX coil might theoretically reach a 40- to 35-degree dew point, but below roughly a 35-degree dew point, coil freezing takes over. Icing is the true barrier of DX dehumidification, and no product changes it. In most applications, a 55-degree dew point is a realistic expectation. The limits are covered in the dehumidification white paper.
How do I improve dehumidification in a constant-volume system without replacing equipment?
Add capacity modulation to the lead stage. In constant-volume comfort systems, a single APR Control on the fixed lead compressor stage extends runtime at part load, which is where humidity problems live. Airflow reduction toward the low end of the acceptable range helps too, but modulation addresses the cause: capacity that exceeds load. This is a refrigerant-side retrofit: no controls integration, no equipment replacement. See also the RSES Journal article Resolving High Humidity.
Why does my space feel muggy even though the thermostat is satisfied?
Because temperature and humidity are satisfied by different things. The thermostat is satisfied by sensible cooling, which an oversized unit delivers in minutes. Moisture removal requires sustained runtime with a cold, wet coil. Short cycles satisfy the first and fail the second; that is the signature of surplus capacity. Load matching with the APR Control converts that surplus into the runtime dehumidification requires. See humidity control.
Is the APR Control used in grow rooms and other controlled-environment spaces?
Yes. Indoor agriculture, and other spaces where temperature and humidity must hold tight tolerances, are established application areas. See the indoor agriculture page and the Stratus grow-rooms field study. The indoor grow rooms white paper covers the application in depth.
Coil Freezing & Low-Load Protection
Why does an evaporator coil freeze at low load?
Less heat entering the coil means suction pressure falls, and with it the refrigerant's saturation temperature. Below 32°F saturation, condensate on the coil freezes; ice blocks airflow, load drops further, and the freeze snowballs. Always rule out airflow problems (dirty filter, blocked coil, blower faults) and low charge first. But when those check out, the cause is load below the compressor's minimum capacity, and the durable fix is capacity modulation that holds suction pressure up. See coil freeze protection.
How does the APR Control prevent coil freezing?
It regulates suction pressure directly: passive evaporator freeze protection, typically holding about 40°F saturated suction on R-410A systems, adjustable by model. In Rawal's documented bench series, 42 of 154 baseline runs (27%) ran below the 40°F setpoint and ten ran below freezing, as low as 24.2°F saturated suction, at ordinary operating conditions. With the APR Control active: zero runs below freezing. The coil cannot follow a vanishing load down through the frost line, because the APR Control diverts capacity before suction pressure gets there. The freeze-exposure data is in the white paper library.
What causes low suction pressure when the cooling load drops?
The load itself. Less heat entering the evaporator means less refrigerant boiling off, and suction pressure falls with it. If the compressor's minimum capacity is still greater than the actual load, suction pressure keeps falling toward the low-pressure cutout and the coil-freezing range. First rule out the impostors: low charge, dirty filters or coils, blower and damper faults. When those check out, the condition is genuine surplus capacity, and the durable fix is capacity modulation that holds suction pressure at setpoint. Start from the symptom you are seeing.
My unit trips its low-pressure switch when the load drops. What should I do?
First rule out what mimics low load: low charge, dirty filter or coil, blower and damper faults. Verify charge and superheat before concluding anything. If the load genuinely falls below the compressor's minimum, the answer is capacity control, not a lower cutout setting. The APR Control holds suction pressure at setpoint continuously, so the compressor keeps running at reduced capacity instead of riding down to the trip, short-cycling on the switch, and accumulating starts. See HVAC system reliability.
Can the APR Control prevent freeze-stat lockouts?
Yes: by removing the condition that trips them. Freeze-stats and low-pressure switches trip when low load drives coil temperature and suction pressure down; the APR Control unloads the compressor before suction pressure gets there, holding it at setpoint. In Rawal's documented bench series, baseline runs went below freezing at ordinary operating conditions; with the APR Control active, zero runs did. The system still needs to be properly charged, maintained, and configured; the valve prevents low-load trips, not all trips. See coil freeze protection.
Can I run a DX coil at reduced airflow (VAV service) without freezing it?
Yes, with per-circuit suction-pressure regulation. Reduced airflow reduces coil load, which drags suction pressure toward the frost line; airflow minimums alone leave a narrow, fragile margin. An APR Control on each refrigeration circuit holds each circuit's suction pressure at setpoint regardless of airflow. On multi-circuit and stacked coils, reduced airflow also distributes unevenly across the coil face, loading circuits unequally; that is the reason Rawal recommends every circuit, not just the lead. See the VAV systems page.
What suction pressure does the APR Control hold?
Each model has a factory setpoint: approximately 118 psig (about 40°F saturated suction) for standard R-410A models, with corresponding settings for R-454B and other models. The setpoint is field-adjustable, and factory settings by model are published in the APR Control Troubleshooting Guide. Service resources are at service & start-up.
Compressor Protection & Reliability
What causes compressor floodback at low load, and how do I prevent it?
When coil load vanishes, a bleed-type expansion valve cannot meter below its bleed floor, and the evaporator overfeeds. That happens with or without capacity control; it is caused by the missing load, not by any control device. The APR Control protects the compressor at this boundary: its mixing tee blends the warm diverted gas into the suction stream, restoring compressor superheat even when the evaporator runs wet to the exit. In instrumented testing, evaporator-exit superheat sat at zero while the compressor inlet held 12–13°F of superheat; the compressor stayed protected while the system carried a very light load. The instrumented data is in the white paper library.
Does frequent cycling shorten compressor life?
Cycling is a recognized stress driver: inrush heating, starts without a full oil film, oil migration during off-cycles. The APR Control reduces cycling by keeping the compressor running continuously at reduced load. In bench testing, compressor dome temperature, compression ratio, and amp draw were lower with the APR Control active in all 24 matched run pairs, with the reductions scaling with modulation depth. Rawal does not publish a compressor-life multiplier: the measured record shows reduced operating stress, and that is exactly what is claimed. See HVAC system reliability.
Does the APR Control reduce compressor failures?
Every start is the highest-stress event a compressor endures, so fewer starts means less wear. In an independent field study, APR modulation cut total compressor starts 77% (951 to 218), with zero compressor failures since install (Independent Field Study). See HVAC system reliability.
Does diverting hot discharge gas stress the compressor?
No, because the gas doesn't return hot. The diverted discharge gas surrenders its heat in the APR Control's desuperheating chamber and returns to suction cool: in instrumented testing the chamber ran 67–86°F while compressor discharge ran 125–200°F. Measured compressor dome temperatures fall, not rise, under modulation, in every matched bench pair. The measured data is in Why the APR Control Is Not Hot Gas Bypass.
What is the difference between evaporator flooding and compressor flooding?
They are distinct events with the APR Control's mixing tee as the boundary. Evaporator flooding (refrigerant still mixed-phase at the coil exit) is caused by light load meeting an expansion valve that cannot close far enough. Compressor flooding (liquid reaching the compressor and washing oil from the sump) is the damaging one. The APR Control stops the second: the tee restores superheat to the gas the compressor actually inhales. The protection boundary is documented in the white paper library.
Energy & Power
How much energy does the APR Control save?
Two measured components. Compressor: manufacturer lab testing measured up to 16% lower compressor power draw at part load, at identical conditions, at the deepest modulation tested. Fan: with a supply-fan VFD, part-load fan energy savings typically run 40 to 60%, and the airflow reduction the APR Control makes possible cut supply-fan power 80% in bench testing (1,543 W at the factory 4,000 CFM down to 304 W at 1,500 CFM). It matters because about 90% of operating hours are part load. Run your own numbers with the ROI estimator.
Does the APR Control reduce fan energy?
It can, substantially, in applications designed to reduce airflow at part load. The APR Control's suction-pressure regulation is what makes deep airflow reduction safe on a DX coil, and fan power falls steeply with airflow: in bench testing, supply-fan power fell from 1,543 W at 4,000 CFM to 304 W at 1,500 CFM. In constant-volume applications the fan savings don't apply; the compressor savings still do. See energy efficiency.
Doesn't diverting compressor discharge waste energy, like hot gas bypass?
No; this is the decisive difference between the two. Hot gas bypass keeps the compressor producing full capacity at full power and destroys the excess. The APR Control unloads the compressor: compression ratio and amp draw fall as it modulates. One burns full power to counterfeit a load; the other reduces power to match the real one. The measured comparison is in Why the APR Control Is Not Hot Gas Bypass.
Why doesn't Rawal lead with EER numbers?
Because EER is a full-load laboratory metric, and buildings live at part load. A fixed-capacity system's rated EER says nothing about the hours it spends cycling against a light load, which is where the APR Control operates. Measured part-load compressor draw and fan energy describe what a building actually pays for; those are the numbers Rawal publishes. See energy efficiency.
Can the APR Control contribute to energy-efficiency programs or tax deductions?
Capacity modulation can contribute to whole-building efficiency measures, and eligibility for a specific incentive or deduction (including the federal 179D commercial building energy deduction) depends on the applicable program and project. Talk to a Rawal Devices Engineer about how APR Control retrofits fit qualifying projects. Start with a free engineering consultation.
Codes & Standards
ASHRAE 90.1 and the IECC restrict hot gas bypass. Does that affect the APR Control?
No. The restriction distinguishes the APR Control from hot gas bypass. ASHRAE 90.1 (Section 6.5.9) and the IECC's Hot Gas Bypass Limitation (Section C403.3.3 in the 2021 edition; C403.6.5 in the 2024 edition) limit hot-gas-bypass capacity unless the system has multiple steps of unloading or continuous capacity modulation. The APR Control is continuous capacity modulation, and it is not hot gas bypass: it reduces compressor power draw rather than maintaining it. As with any code question, the authority having jurisdiction makes the final call; Rawal's engineering support can provide documentation for submittals. The white paper Why the APR Control Is Not Hot Gas Bypass walks through the code text and the measured distinctions.
What do the energy codes actually say about hot gas bypass?
The model text reads: “Cooling systems shall not use hot gas bypass or other evaporator pressure control systems unless the system is designed with multiple steps of unloading or continuous capacity modulation.” Even then, bypass capacity is capped: 50% of total rated capacity for systems of 240,000 Btu/h or less, and 25% above that. Those thresholds have been stable across recent code cycles, but the section number moves by edition: ASHRAE 90.1 keeps it at Section 6.5.9, while in the IECC it is C403.3.3 in the 2021 edition, C403.6.5 in the 2024 edition, and C403.4.6 in earlier editions. The restriction exists because hot gas bypass maintains full compressor power at part load. Cite the edition your jurisdiction enforces. See Why the APR Control Is Not Hot Gas Bypass.
Does the APR Control qualify as “continuous capacity modulation” under the code language?
The APR Control modulates capacity continuously and proportionally over its range, not in steps, self-regulated by suction pressure. That is the operating behavior the code language describes. As with any code question, the authority having jurisdiction makes the final call; Rawal's engineering support can provide documentation for submittals. For submittal documentation, see specs & submittals.
Applications: VAV, DOAS, Make-Up Air & More
In a constant-volume packaged unit, where does the APR Control go?
On the fixed lead compressor stage, with one APR Control. That is Rawal's standard practice for constant-volume comfort cooling: the lead stage becomes the modulating stage and upper stages trim above it. The lead must stay fixed; lead-rotation schemes re-break the arrangement by moving the load away from the modulating circuit. See the rooftop units page.
In VAV, DOAS, and make-up air systems, should capacity control go on every refrigeration circuit or just the lead?
Every circuit. Lead-only control fails these applications four ways: staging is too coarse for continuously varying loads; lead rotation moves the load off the modulating circuit; split and interlaced coil circuiting divides load unevenly between circuits; and at reduced airflow, air maldistributes across the coil face so each circuit sees a different load. A modulating unloader on each circuit, each sensing its own suction pressure, is the matched response. This is Rawal's application position from three decades of field experience. The all-circuits justification is in the white paper library.
What is air-side maldistribution, and why does it matter at reduced airflow?
At reduced airflow, the static pressure differential across the coil collapses, and air stops distributing evenly across the coil face: more air through one section, less through another, and worse on stacked coils. Circuits then carry unequal loads, and a starved circuit's suction pressure falls toward frost while its neighbors run normally. Per-circuit APR Controls respond to each circuit's own condition, so the capacity control matches a maldistributed coil circuit by circuit. The maldistribution analysis is in the white paper library.
Can a DX dedicated outdoor air system hold a stable discharge temperature as outdoor conditions swing?
Yes, with continuous capacity modulation. In instrumented testing of an R-454B DOAS unit, the APR Control held its suction-pressure band across entering air ranging from the 60s°F to over 100°F, with the compressor running more than 99% of the time across the logged tests: steady operation instead of cycling through widely varying entering conditions. See the DOAS page.
How do I keep a DX make-up air unit stable in winter and shoulder seasons?
Make-up air is the hardest duty for fixed-capacity DX: 100% outdoor air means the load swings with the weather, hour by hour. Continuous suction-pressure regulation with an APR Control on each circuit lets the unit track those swings while running steadily, instead of short-cycling through every mild afternoon. Pair with the unit's low-ambient controls; the modulation handles the load side. See specialty applications.
Does the APR Control work in single-zone VAV applications?
Yes. Single-zone VAV pairs fan turndown with cooling turndown, and the APR Control supplies the cooling side continuously on the existing fixed compressor. See the VAV systems page.
Can I add capacity control to an existing rooftop unit?
Yes. The APR Control is a refrigerant-side retrofit for equipment you already own: no crane, no curb change, no unit replacement. It is the reason most customers install it, and it also installs on new equipment by OEMs, modifiers, and contractors. See the rooftop units page.
Does the APR Control work on split systems and heat pumps?
Yes, on standard DX split systems and heat pumps as well as packaged and rooftop units. Heat pumps in colder climates are sized for the heating load, which typically leaves them oversized for cooling, so they short cycle all summer. The APR Control adds continuous capacity modulation in cooling, with no impact on rated capacity on the design day. On split systems the suction line size matters for oil return, and heat-pump installations follow a dedicated piping diagram, so Rawal Devices Engineering confirms the selection and configuration with you. See split systems and heat pumps.
Does it work on DX chillers?
Yes, on chillers built from DX refrigerant circuits: air-cooled or water-cooled, with reciprocating or scroll compressors. Modular chillers are a particularly good fit: an APR Control on each circuit lets each respond to its own suction pressure, so the module runs steadily at part load instead of short cycling into low-pressure and low-leaving-water lockouts. In one Washington, D.C. restaurant installation, an APR Control on each 30-ton circuit provided about 67% turndown and ended the lockouts. It does not apply to centrifugal chillers, which have no DX circuit to modulate. For screw-compressor chillers, call Rawal Devices Engineering to review the application. See the chillers page.
Can the APR Control help with mismatched equipment?
Yes. Mismatched equipment is a common application for the APR Control. The classic case: an oversized condensing unit gets installed on an existing air handler, because the old condensing unit failed and the replacement options didn't match, or because the air handler is built into the building and isn't going anywhere. Now the compressor moves more refrigerant than the evaporator can boil off. The APR Control absorbs exactly that mismatch: it diverts a portion of the refrigerant mass flow, matching what the compressor delivers to what the evaporator needs, continuously and self-regulated by suction pressure. Left uncorrected, that same mismatch shows up as low suction pressure, a freezing coil, tripping, and short cycling, and it often gets blamed on everything except the mismatch. One boundary: the APR Control trims surplus, it can't add capacity; an undersized condensing unit on a big coil is a different problem it won't fix. Mismatched-equipment applications should be sized by Rawal engineering support against the actual pairing: 800.727.6447. Or start with a free engineering consultation.
In high outdoor-air spaces, do I still need reheat if I have the APR Control?
Often yes; they do different jobs. High air-change applications carry an airflow-driven surplus load that modulation absorbs, and a reheat requirement that modulation does not replace: the APR Control matches cooling capacity to the real load, while hot gas reheat tempers the supply air. The two strategies are used together when the application requires both. The high-ACH screening method is in the white paper library.
What equipment does the APR Control work on?
Any standard DX system with a refrigerant circuit to modulate: rooftop units, split systems, heat pumps, DX chillers, and DOAS or makeup air units, from systems as small as 1.5 tons through large multi-circuit equipment. The only exclusion is non-DX equipment, which has no refrigerant circuit to modulate. See compatible systems.
What size systems does the APR Control fit?
The APR Control is always sized to the lead compressor, so it fits systems from small residential-scale equipment up through large staged commercial units. There is no simple catalog tonnage limit; the valve is sized to the lead compressor and its refrigeration circuit, so tell us the lead stage and Rawal Devices Engineering makes the selection. See small systems.
What refrigerants does the APR Control work with?
New and legacy refrigerants: R-410A, the A2L refrigerants R-454B and R-32, and legacy R-22. It has also been applied on others, including R-407C, R-404A, and R-134a. Model families are matched to the refrigerant, so tell us what you have and Rawal Devices Engineering confirms the right model, including current install packages for the A2L transition. See the refrigerants page or try the refrigerant navigator.
Does capacity control work with R-454B and R-32?
Yes. The APR Control is compatible with standard RTU and split systems on new or old refrigerants: R-410A, R-454B, and R-32, plus legacy R-22. Model families are matched to the refrigerant, and Rawal Devices Engineering confirms the right one during the free engineering consultation. Download the R-32 / R-454B spec sheet.
Will the APR Control work on my R-22 equipment?
Yes. Legacy R-22 systems are fully supported, which matters as R-410A and A2L transitions raise the value of extending the life of in-place equipment. Ask Rawal Devices Engineering for the R-22 selection. See the refrigerants page.
Comparisons: Hot Gas Bypass, Variable Speed & Staging
Is the APR Control just hot gas bypass?
No. Hot gas bypass is defined by four properties: it delivers hot gas, it keeps the compressor loaded, it carries an energy penalty, and it adds thermal stress. The measured record inverts all four for the APR Control: the diverted gas surrenders its heat in a desuperheating chamber and returns cool; the compressor unloads (amp draw, compression ratio, and dome temperature all fall); power draw drops at part load; and operating stress decreases in every matched test pair. The full analysis, with the measured data, is the white paper Why the APR Control Is Not Hot Gas Bypass.
Is hot gas bypass bad for efficiency, and is there an unloading method that isn't?
Classic hot gas bypass is a genuine efficiency penalty: the compressor runs at essentially full power while its output is thrown away, which is why energy codes restrict it. The APR Control is the unloading method that isn't: it reduces the compressor's work to match the load, with measured lower amp draw and compression ratio, while delivering the same low-load stability hot gas bypass was historically used for. See energy efficiency.
How is the APR Control different from a variable-speed (inverter) compressor?
Different routes to load matching. Inverter equipment modulates by replacing the compressor and adding power electronics and controls integration. The APR Control modulates the existing fixed compressor externally: a mechanical, self-regulating refrigerant-side device with no electronics, serviceable by any qualified refrigeration technician. For existing equipment, it is the retrofit path; for new equipment, it delivers continuous modulation without the electronics complexity. See the comparison hub.
How does the APR Control compare to a digital scroll compressor?
A digital scroll modulates by periodically unloading the scroll set, a compressor-replacement solution with time-averaged capacity. The APR Control provides continuous refrigerant-side modulation on the compressor already in the unit. No compressor swap, no controller dependency, and the modulation is steady-state rather than pulsed. See the comparison hub.
Should I retrofit an APR Control or replace the unit with two-stage equipment?
Two stages is still step control: 50 or 60 percent jumps, with cycling inside each step. The APR Control provides continuous modulation on the equipment you already own, at a fraction of replacement cost. Where replacement is warranted anyway, an APR Control on the new unit's lead stage still provides what staging alone cannot: continuous load matching between steps. See Retrofit vs. Replace.
Selection, Installation & Service
How is the APR Control sized and selected?
Rawal Devices Engineering sizes every valve to the lead compressor, at no charge, to maximize modulation without compressor termination and without compromising oil entrainment in the suction line. The principle is the same regardless of tonnage: the valve's capacity-modulation tonnage never equals the system or compressor tonnage. One example of the principle at work: a 5-ton lead stage fitted with an APR Control providing 3.5 tons of modulation. Start with the sizing tool, then talk to us. Rawal doesn't quote or sell an APR Control from a form alone; every selection is confirmed in a conversation with our engineering support, against your actual equipment and application.
What does the APR Control's tonnage rating actually mean?
It describes the valve, not the system, and that is the most common misreading. The tonnage rating is the refrigerant mass flow through the APR Control itself; it is not the size of the system the valve gets applied to. You would never apply a 5-ton APR Control to a 5-ton compressor; the valve's rating is almost always less than the rating of the compressor it serves. That's because the valve is sized on oil-return characteristics (how much modulation the suction line can carry while still returning oil), not on the capacity of the equipment. When you read the rating, read it as “how much capacity modulation this valve provides,” never “what size system this valve fits.” Check your application with the sizing tool.
What information does Rawal need to size an APR Control?
Equipment capacity, refrigerant, compressor staging, suction-line size, and the system configuration, plus the problem you are trying to solve. Photographs, model and serial numbers, and piping details all help. Multi-circuit equipment, heat pumps, specialty refrigerants, and unusual operating requirements may call for additional engineering information; Rawal Devices Engineering confirms every selection: 800.727.6447. Or start with a free engineering consultation.
Can I size an APR Control myself?
Start with the sizing tool, then talk to us. The valve's rating is never simply matched to the system's nominal tonnage: oil return and the actual refrigeration circuit determine the correct selection. Rawal doesn't quote or sell an APR Control from a form alone; every selection is confirmed in a conversation with engineering support, against your actual equipment and application.
How is the APR Control installed?
Three refrigerant line connections (discharge, suction, and liquid), typically made in the condensing unit or condensing section, by any qualified refrigeration technician. No electronics, no controls wiring, no crane, no curb change. (The APR‑E Valve adds simple control wiring for the command signal.) See the installation hub, and join the free live pre-installation webinar, held every Monday, Wednesday, and Friday at 9:00 AM Eastern, to walk through it with an engineer.
How long does an APR Control installation take?
Budget approximately one technician day for a typical installation. Actual time varies with the technician, the equipment, the quantity of valves, and the application; experienced installers routinely finish faster. The work is refrigerant-side: recover, braze in three connections, evacuate, recharge, and verify operation. Step-by-step detail is in the installation instructions.
Does installing an APR Control change the system's refrigerant charge?
No. The installation involves recovering and recharging the refrigerant, but the system's charge remains the amount specified by the equipment manufacturer; the APR Control does not require a different charge. See the installation hub.
Can the APR Control be installed on a pump-down system?
Yes. Install a solenoid valve in the APR Control's mixed gas line, wired to enable and disable together with the system's existing liquid line solenoid. The reason: pump down works by driving suction pressure low, exactly the condition the APR Control exists to respond to. Without the solenoid, the valve would open as suction falls and feed gas back to the compressor inlet, and the system would never reach its cutout. Closing the mixed gas line in step with the liquid line solenoid lets pump down finish exactly as designed. Contact Rawal Devices engineering support to review the arrangement for your system. Or start with a free engineering consultation.
Can a solenoid valve be used with the APR Control on a system that isn't pump down?
Yes, as a staging control. Some systems need deep modulation at the second, third, or fourth stage, but the piping can't take any modulation at first stage, where oil return is critical. The arrangement: wire a solenoid valve so it opens only when more than one compressor is running. With a single compressor on, the APR Control stays out of the picture and first-stage oil return is never touched; once additional stages come on, the solenoid opens and full modulation is available. It's another engineered solution; Rawal Devices engineering support designs the arrangement to your staging and piping: 800.727.6447. Or start with a free engineering consultation.
Can the APR Control be adjusted in the field?
Yes. The suction-pressure setpoint is field-adjustable; each model ships at a factory setting published in the Troubleshooting Guide. Rawal's adjustment resources cover the procedure for optimizing a system in service. See service & start-up resources.
What maintenance does the APR Control need?
It is a mechanical, self-regulating device with no electronics; there is nothing to program and no controller to fail. Include it in normal preventative maintenance checks; the Troubleshooting Guide covers what to verify. Its presence also makes PM more effective: a system that runs steadily at part load instead of short-cycling is an easier system to assess. Service resources are at service & start-up.
Is the APR Control in stock?
In stock and ships fast. Selections are confirmed by Rawal Devices Engineering before you order, so the part that arrives is the right one for your system. To order or check availability, contact Rawal Devices.
What is Rawal Devices' warranty?
Rawal Devices provides a 1-year parts warranty from date of purchase on the APR Control and APR‑E Valve, and every installation is backed by live engineering support from sizing through start-up and after. One service note: the Liquid Injection Valve is factory-set; field-adjusting it voids the warranty. Adjustment, when needed, is made at the Compression Ratio Reduction Valve only. Contact Rawal Devices with warranty questions.
Will installing the APR Control affect my equipment's warranty?
Equipment warranty terms vary by manufacturer and by what the warranty covers, so check with your equipment manufacturer or ask us about your specific unit before you install. Two facts worth knowing when you do: HVAC manufacturers offer the APR Control as a factory-installed option on new equipment, and the APR Control installs with three refrigerant connections without altering the compressor or its controls. A Rawal Devices Engineer can talk through your manufacturer's terms with you: 800‑727‑6447. Or contact Rawal Devices.
How do I troubleshoot a system with an APR Control?
Start with the APR Control Troubleshooting Guide for Service Technicians; it covers operating checks, factory settings by model, and isolation procedures. See also service & start-up resources. Rawal technical support is available at 800.727.6447 or [email protected], Monday–Thursday 8:00–5:00 and Friday 8:30–4:00 Eastern.
Does modulating capacity cause oil-return problems?
Oil circulation is a line-sizing question, and it is addressed at selection: the valve and suction line are chosen together so oil entrainment is maintained across the modulation range. There is no universal “never unload below 50%” rule; proper selection is application-specific, with turndown reaching upwards of 80%+ depending on unit configuration, oil return maintained. Check your circuit with the sizing tool.
Service Diagnostics: Is the APR Control the Problem?
Is the APR Control a suitable replacement for a low ambient kit?
No. They solve different problems on different sides of the system. A low ambient kit maintains head pressure when outdoor temperature falls, so the expansion valve keeps an adequate pressure differential. The APR Control regulates suction pressure, matching capacity to the load. One manages the condenser side against cold weather; the other manages the load side against light load. Applications that face both conditions (make-up air units are the classic case) use both, working together. See specialty applications.
Does the APR Control need a low ambient kit in order to function?
No. In most applications the APR Control needs no low ambient kit; it is self-regulating and functions on the system as built. The simple rule: if the unit needs a low ambient kit anyway (whether an APR Control is installed or not), put one in; the APR Control doesn't change that requirement in either direction. And in certain special applications, a low ambient kit can be advantageous even where the unit wouldn't otherwise call for one, to maintain a slightly higher-than-normal head pressure. Call Rawal Devices engineering support to discuss your application. Or start with a free engineering consultation.
Can the APR Control help in high ambient temperature conditions?
Yes, as compressor protection. When a system runs at higher than design-day conditions, high superheat and a lack of capacity at the coil follow. The APR Control's liquid injection valve keeps the gas temperature entering the compressor reasonable, which keeps discharge refrigerant gas temperature down, protecting the compressor from overheating on days hotter than the system was designed for. Be clear about what this is and isn't: it is protection, not capacity. The APR Control does not add capacity at the evaporator; on an above-design day the system is still short on cooling. What it does is help the compressor survive the conditions forcing it to run flat out. The liquid injection function is explained in How It Works.
Is a failed APR Control a reason for high head pressure?
No. An APR Control that fails closed leaves the system operating exactly as built without one; it cannot add head pressure. And when the valve is open, it diverts a portion of discharge gas away from the condenser, which reduces the condenser's load. A failed APR Control is not a cause of high head pressure. High head pressure has the usual causes: dirty condenser coil, condenser fan problems, air recirculation, overcharge, or non-condensables. Look there. Diagnostic resources are at service & start-up.
Is an operating APR Control a reason for high head pressure?
No; the measured record shows the opposite. When the APR Control modulates, discharge pressure and condensing pressure fall, because less refrigerant mass flow reaches the condenser. In bench testing, head pressure dropped in every modulating run. If you're reading high head pressure on a system with an APR Control, the cause is elsewhere. The bench data is in the white paper library.
Is an APR Control a reason for low suction pressure?
No; holding suction pressure up is the entire job of the valve. The APR Control opens when suction pressure falls below its setpoint and modulates to hold it there; it has no mechanism for pulling suction pressure down. If suction pressure is low on a system with an APR Control, either the load has fallen beyond the valve's modulation range (a condition the system would have reached far sooner without it), or the cause is one of the usual suspects: low charge, low airflow, a dirty filter, or a metering-device problem. Diagnostic resources are at service & start-up.
Can the APR Control cause a restriction in the system?
No. The APR Control is not installed in the system's main refrigerant path; it connects in parallel, through three tee connections to the discharge, suction, and liquid lines. The refrigerant serving the evaporator and condenser never passes through the valve. Closed, it carries no flow at all and the system's circuit is exactly as the manufacturer built it. A restriction lives in the series path: filter-driers, expansion-valve screens, kinked lines, not in a parallel-connected device. See How It Works for the parallel piping arrangement.
Can the APR Control increase superheat?
Yes, at the compressor, by design. The mixing tee blends warm diverted gas into the suction stream, manufacturing compressor superheat even when evaporator-exit superheat sits at zero. Under modulation the compressor typically sees superheat in the teens, approaching 20 degrees at deep modulation, the point where the liquid injection valve begins metering to cap it. Elevated compressor superheat on a modulating system is normal operation, not a fault. The superheat mechanism is explained in How It Works.
The APR Control is sweating. Does that mean it's broken?
No; the valve is telling you something about the system, not about itself. A sweating APR Control is usually a symptom of low refrigerant charge. Here's the chain: a lack of charge produces high superheat coming out of the evaporator, so the APR Control's liquid injection valve works to bring that superheat under control at its 20-degree point, and doing that much cooling typically drops the desuperheating chamber's temperature below the dew point of the surrounding air. The moisture on the valve is condensation, exactly like a cold glass of water in summer. Check the system's charge and superheat before condemning the valve; the APR Control is doing its job, and the sweat is it working overtime to cover for a charge problem. More service checks at service & start-up.
I've installed an APR Control, but I'm still getting high humidity. Why?
Start with the simple possibility: an adjustment. The APR Control's factory setpoint is chosen as the best setpoint for most of the country, which doesn't make it perfect for every application. What the setpoint is meant to achieve is maximum modulation before compressor termination, and no modulation during high load; the factory settings usually accomplish exactly that, but some applications need an adjustment.
If the setpoint checks out, look at the building, because not every humidity problem is a capacity problem. Common culprits: a high percentage of outside air with a continuously running fan; compressor off-time that runs too long; and conditions no modulating compressor technology can address at all, such as exhaust fans without makeup air, or a building running at negative pressure, pulling humid air in through every crack. In many buildings these problems existed long before the APR Control was installed and were never examined. If humidity persists after adjustment, Rawal technical support at 800.727.6447 can help you sort which kind of problem you have. See also the RSES Journal article Resolving High Humidity.
APR‑E Valve & Controls
How precise is the APR‑E Valve's discharge air control?
The APR‑E Valve holds discharge air temperature to ±1°F on DAT control, driven by your BAS or a stand-alone controller. It delivers precise discharge air on standard equipment that would otherwise need a far more expensive custom unit: chiller dreams on a DX budget. See the APR‑E Valve page.
Can the APR‑E Valve integrate with my building automation system?
Yes. The APR‑E Valve takes a 0 to 10VDC or 4 to 20mA command signal from a building automation system or a stand-alone controller, and modulates capacity to hold your discharge air setpoint. See the APR‑E Valve page.
Deciding & Getting Help
How do I know if my AC or rooftop unit is oversized?
The clearest sign is short cycling: the unit cools the space quickly, shuts off, and restarts a short time later, so it runs in short bursts instead of long, steady cycles. Watch for humidity that stays high even when the air feels cool, coils that frost or freeze at low load, uneven room temperatures, and comfort complaints and service calls that keep climbing. Together these point to equipment that is oversized for the load it actually carries most of the year. The fix is continuous capacity modulation: an APR Control lets the system run at part load instead of cycling. Not sure? A free engineering consultation will confirm it.
When is an APR Control a good solution?
When a fixed-capacity DX system has more capacity than the space needs for a substantial share of its operating hours. The classic signs: short cycling, temperature swings, humidity that stays high while the thermostat is satisfied, and low-pressure or freeze trips at light load. The classic applications: oversized equipment, mismatched equipment, VAV, DOAS, make-up air, heat pumps in cooling, and modular DX chillers. It is not a fix for undersized systems, charge problems, or building-envelope issues; it trims surplus and cannot create capacity. Start from the symptom you are seeing.
Who should consider an APR Control?
Contractors solving callbacks on humidity, freezing, and nuisance trips; engineers specifying VAV, DOAS, and make-up air systems that need continuous modulation; facility managers with oversized or short-cycling equipment they don't want to replace; and OEMs, distributors, and authorized equipment modifiers offering factory-installed capacity modulation. If a DX system runs at part load most of its hours (and about 90% of operating hours are part load), the APR Control is worth evaluating. Pick your role on the who we help page.
Can the APR Control be factory-installed on new equipment?
Yes. HVAC manufacturers offer the APR Control as a factory-installed option, and factory-authorized equipment modifiers install it on new equipment before delivery, so new DX equipment can ship with continuous capacity modulation built in. The same valve is available as a field retrofit on existing equipment. See factory install.
When should I contact Rawal Devices engineering?
Any time the selection is not routine. Every APR Control selection is confirmed with Rawal Devices Engineering before it ships, at no charge. Call especially for multi-circuit equipment, heat pumps, pump-down systems, specialty refrigerants, unusual staging, mismatched equipment, or turndown requirements beyond standard selection: 800.727.6447, or start a free engineering consultation.
The Evidence & White Paper Library
What testing supports Rawal's claims about the APR Control?
Four bodies of evidence, each identified as what it is. First, an instrumented psychrometric-chamber bench test series on R-410A equipment, using matched runs at identical conditions with a second, unmodified compressor circuit as an internal control. Second, instrumented testing of an R-454B dedicated outdoor air system at an equipment manufacturer's R&D laboratory. Third, independent field studies, including a Virginia healthcare facility (Independent Field Study) and the Stratus grow-rooms study. Fourth, more than 30 years of field application. The white paper library documents methods, data, and results.
Is the APR Control patented?
The APR Control was patented in 1993 (U.S. Patent No. 5,240,651) and has more than 30 years of field application since. Rawal Devices has manufactured and supported the technology continuously since its original development. Read the patent at Google Patents.
How does Rawal label its results?
Every result in the white paper series is labeled as measured, modeled, or expected, and claims are attributed to the specific product tested (APR Control or APR‑E Valve), never silently generalized between them. Where a finding is field experience rather than laboratory data, the papers say so. Where the data cannot support a conclusion, the papers say that too.
This knowledge base follows the same discipline. Each claim belongs to one of four classes: measured (laboratory and test-stand data), field observed (customer installations and independent field studies), engineering principle (what the mechanism does by design), or application guidance (what Rawal recommends). The wording of each answer names its class: “in bench testing,” “in an independent field study,” “by design,” or “Rawal recommends.” Read the papers in the white paper library.
Can Rawal's results be independently verified?
The papers document instrumentation and method in enough detail to repeat the measurements, and where a specific verification would settle a question, the papers state the protocol and leave it open to any party. Rawal has published its verification paths rather than asking readers to take results on authority. Methods are documented in the white paper library.
Do results measured on test units apply to my system?
The direction of the results generalizes; the magnitudes are application-specific. The mechanism (diversion, desuperheating, compressor unloading, suction-pressure regulation) is the same on any DX system the APR Control is correctly applied to, so the direction of each benefit travels. Rawal states magnitudes only where they were measured, and sizes expectations to your application through its engineering support rather than quoting one unit's numbers as universal. Or start with a free engineering consultation.
Where can I read the white papers?
In the white paper library, covering bench characterization, power reduction, the refrigerant-side mechanism, compressor operating stress, freeze exposure, dehumidification, DOAS verification, all-circuits application justification, maldistribution, high-ACH applications, and why the APR Control is not hot gas bypass.
Glossary
Turndown: how far a system can reduce its capacity below rated maximum. APR Control reaches upwards of 80%+ depending on unit configuration; specially engineered applications with oil management have reached as high as 98%.
Modulation: continuously varying capacity to match load, as opposed to switching on and off.
Short cycling: frequent on/off compressor cycles caused by oversized capacity satisfying the space quickly and restarting.
Part load: any operating condition below design day. Roughly 90% of operating hours are part load.
Design day: the peak conditions a system is sized to meet, occurring only a few days of the year.
Hot gas bypass: a false-loading capacity-control method that keeps the compressor fully loaded and disposes of the excess. The APR Control is not hot gas bypass; it unloads the compressor.
Desuperheating: removing the heat of compression from discharge gas. The APR Control desuperheats diverted gas before returning it to the compressor suction.
Floodback: liquid refrigerant reaching the compressor, washing oil from the sump. The APR Control's mixing tee restores suction superheat to protect against it.
A2L: the class of mildly flammable, lower-GWP refrigerants (R-454B, R-32) replacing R-410A.
DOAS: dedicated outdoor air system, conditioning high volumes of outside air.
VPD: vapor pressure deficit, the humidity-and-temperature window that controlled-environment crops depend on.
Oil entrainment: keeping compressor oil moving through the refrigerant circuit at low capacity, a factor in how APR Control is applied.
Question we did not answer here?
Ask a Rawal Devices Engineer directly. Describe your equipment and your question, and we respond within one business day, sizing on us.
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