A crankcase pressure regulator is designed to prevent compressor suction pressure from rising above what value?

• A. The CPR setpoint
• B. The ambient pressure
• C. The liquid line temperature
• D. The discharge pressure

Answer: (A)

The main idea here is that a crankcase pressure regulator keeps the pressure inside the compressor crankcase from rising past a set value by venting vapor back to the suction side when that pressure is reached. The regulator is designed to sense crankcase pressure and open at its preset point—the CPR setpoint—so it can bleed off excess vapor and prevent further pressure increase. This protects lubrication, reduces oil foaming and carryover, and helps maintain stable compressor operation.

Ambient pressure, liquid line temperature, and discharge pressure aren’t what the CPR actively controls. Ambient pressure isn’t managed by the regulator, liquid line temperature is a temperature, not a pressure limit, and discharge pressure is on the high-pressure side, which the CPR isn’t designed to regulate.