Field reference
Service & Startup
A plain-language field reference for starting up, adjusting, and troubleshooting the APR Control. The install package for your refrigerant is the authority on procedure; this is the quick version, and a Rawal Devices Engineer is one call away.
Call us before you turn anything. A real engineer answers, no queue: 800‑727‑6447. Have the equipment model, refrigerant, APR Control model number, the symptom, and your pressures ready.
Field PDFs
Charging & start-up
- Charge to the equipment manufacturer's spec. The APR Control does not change the charge the unit needs for design-day operation
- On start-up in full cooling, the unit should make its rated capacity as normal
- As the load drops and suction pressure falls to the setpoint, the APR Control begins to modulate, so the compressor keeps running at reduced capacity instead of cycling off
- The APR Control comes factory preset (about 120 psig for R-410A, roughly a 40°F evaporator coil): a set-it and forget-it default for standard DX comfort cooling
Adjustment: when, why, how
For most standard DX comfort cooling, the APR Control does not need adjustment: it ships factory set. You adjust it to tune the modulation point for the application, or when low-load runtime is still not what the space needs.
When to adjust
- Low-load operation does not pull suction pressure low enough for the APR Control to activate
- Case 1, colder discharge air or more dehumidification: tune the modulation point to extend low-load runtime so the coil keeps working. Adjustment direction is model-specific; follow the install package for your unit
- Case 2, coil icing or low-temperature cutout risk (VAV, MUA, or DOAS): tune the modulation point to keep the coil above icing at low load. Adjustment direction is model-specific; follow the install package for your unit
How it adjusts
- Adjust the screw under the cap on the Compression Ratio Reduction Valve on the discharge line
- On R-410A models, roughly 5 psi per full turn, within about a 95 to 130 psi range; direction and psi-per-turn vary by model number
- Goal: maximum modulation before compressor termination
Do not adjust the Liquid Injection Valve. Adjusting it voids the Rawal Devices warranty. If you are not sure which port you are looking at, call before you turn anything.
Is it the APR Control, or the system?
Most calls that get blamed on the APR Control are really airflow, charge, or metering. The quickest way to tell them apart: the APR Control only modulates at part load and never reduces the unit's rated capacity on design day. So a hot-day, cannot-make-capacity complaint is almost never the APR Control.
Check the system first
- Airflow: dirty filters, coils, blocked returns, or a failing blower
- Charge and the metering device (TXV)
- Cannot hold temperature on a design day: a capacity, charge, or airflow issue, not the APR Control
Then look at the APR Control
- Coil icing or low-temp cutout at low load (Case 2): the modulation point needs adjustment to keep the coil above icing; confirm the direction against the install package
- Space stays humid (Case 1): the compressor may be satisfying too fast; tune the modulation point to extend low-load runtime
- Confirm nobody adjusted the Liquid Injection Valve
The current install package for your refrigerant is the authority on procedure and setpoints, and a Rawal Devices Engineer will confirm the specifics for your unit.
Not sure? Call before you turn anything.
A real engineer answers, from install through start-up and service.
Call 800‑727‑6447[email protected] · 800‑727‑6447 · rawal.com