Crankcase pressure regulating (CPR) refrigeration valves are used to limit the amount of refrigerant entering the compressor.
Why limit the refrigerant?
Refrigeration compressors a designed to pump a specific maximum volume of refrigerant.
If the volume exceeds this limit, the compressor motor becomes overloaded and the amperage increases.
Continuous operation under these conditions can cause damage and failure.
This is especially true on low temp freezers.
Very low evaporator temperatures have very low evaporator pressures. A properly sized compressor is designed to pump these lower pressures.
The problem arises when the evaporator temperature is not low. Perhaps after an extended defrost or repair, the evaporator has become very warm.
What happens when the condensing unit starts?
The amount of pressure returning to the compressor is much higher than the compressor can tolerate, resulting in compressor overload!
The compressor eventually trips safety overloads or breakers. The evaporator stays warm. Resetting the overloads only repeats the cycle.
CPR valve to the rescue!
Installing a CPR valve takes care of the problem.
The valve can be adjusted to limit the amount of refrigerant allowed into the compressor.
What's the best way to properly adjust the valve?
Attach your amp meter on the compressor lead. Slowly close the valve while the condensing unit is running.
The amps should slowly decrease as you close the valve.
Continue closing until the amperage falls below the run load amperage (RLA) displayed on the compressor data plate.
This it! The CPR valve is now properly set.
Another practical use for these refrigeration valves is found on hot gas defrost systems.
The CPR valve helps disperse any liquid refrigerant that may flood back from the evaporator after defrost.
I always installed a CPR valve on freezer cases, it extended the life of the compressor.
The gentle hissing as the valve metered the refrigerant was music to my ears!
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