A crankcase pressure regulator (CPR) is a common accessory added to many low-temperature refrigeration applications, such as walk-in and reach-in freezers. They are designed to prevent the compressor's motor from overloading when its crankcase pressure rises above its designed working pressure. On many low-temperature applications, this can occur during or after a defrost cycle, or after a normal shutdown period. The CPR is an outlet pressure regulator and will not allow the crankcase pressure to rise above a predetermined level.
Typically the CPR is installed in the suction line between the compressor and the evaporator. Normally, there are no other components installed downstream, between the outlet of the CPR and the compressor. This is to ensure that the outlet of the CPR senses the true crankcase pressure of the compressor.