By Problem
Frozen Coils & Liquid Slugging
Two very different situations drive the same failure: an evaporator coil that ices over, and a compressor that takes a slug of liquid refrigerant. The APR Control has passive evaporator freeze protection that solves both, whether the unit is oversized or fighting low airflow.
Why coils freeze and compressors slug
An evaporator coil ices over when it runs colder than freezing, and a compressor gets slugged when refrigerant reaches it as liquid instead of vapor. Both come down to suction pressure dropping too low, and two common situations push it there:
Oversized Units at Low Load
For most of the year the system has far more capacity than the space needs. At that low load, suction pressure falls, the coil drops below freezing, and frost builds. Short cycling makes it worse.
Units with Low Airflow
When airflow across the coil drops, from a dirty filter, VAV turndown, undersized ducts, or a fan problem, the refrigerant picks up less heat and does not fully boil off. The coil runs toward freezing, and unboiled liquid slugs back to the compressor.
Once the coil ices, the system loses capacity and can shut down. And liquid slugging, also called floodback, washes oil out of the compressor and mechanically hammers it, one of the most common causes of compressor failure.
How the APR Control protects the coil and the compressor
The APR Control is a pressure-activated valve that reads suction pressure, the exact signal that a coil is heading toward freezing. As suction pressure falls, the APR Control modulates capacity to hold the coil in its safe operating range, keeping the evaporator above freezing and the returning refrigerant fully evaporated. That passive evaporator freeze protection is what guards the compressor against liquid slugging and floodback.
Oversized units
The APR Control matches capacity to the real load, so suction pressure never drops far enough to ice the coil. The system runs at part load instead of driving itself below freezing.
Low airflow
As airflow drops and the coil starts to run cold, the APR Control holds suction pressure in its safe range, keeping the coil above freezing and making sure the compressor sees vapor, not liquid.
From the field
Keeping a coil above freezing at very low load
In an emergency cold-storage application, standard wall-mounted DX kept freezing its own coil at very low load. The APR Control held suction pressure to keep the coil above freezing, and it was valued for being available with no lead time. See more in the Case Studies.
Fighting a frozen coil or a slugging compressor?
Tell us what the coil and compressor are doing, and we size the fix, on us.
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