A CPR or crankcase pressure regulator is nothing more than a pressure reducing valve. When installed on a compressor suction inlet and properly adjusted, the CPR will prevent the compressor suction pressure from ever rising above the CPRs setting. The CPR will help prevent refrigeration compressor from overloading during startup on refrigeration systems that may experience heavy load conditions such as a freezer after a defrost cycle. Coolers that experience startup problems related to extreme loads may also utilize a CPR.
Compressors have a maximum suction pressure that they are designed to handle. An overloaded compressors amp draw will exceed FLA causing the compressor to cycle on it’s overcurrent protection. A badly overloaded compressor may not start at all. A zero degree freezer may have an operating suction pressure of 25 PSIG. When this freezer comes out of defrost, the evaporator may be 50 degrees and have a suction pressure of 105 PSIG. This suction pressure will be too high for most low-temperature compressors to start against. In this case, a CPR installed at the compressor inlet and adjusted to 45# will allow the compressor to start without overloading. Once the compressor starts and the evaporator begin to cool down, the suction pressure will fall below the CPRs 45# set point and open completely to allow proper suction gas flow.
When selecting or adjusting a CPR some important things must be considered. The suction pressure setting of the valve must be low enough to prevent the compressor from overloading. If the CPR is undersized or is set too low the suction gas flow to the compressor will be too restricted. This will reduce system capacity and could cause compressor overheating. To adjust the CPR, put the system into a defrost cycle to heat up the evaporator coil. Install an amp meter on the compressor making sure that you are reading only the compressors current draw. Start the compressor and adjust the CPR until the compressor is drawing no more than FLA. This procedure may need to be repeated as the suction pressure may fall quickly once the compressor is started. Though a CPR may become restricted or fail, it is not likely that it will come out of adjustment.