What does an evaporator pressure regulator primarily do?

• A. It will not allow the evaporator pressure to drop below its setpoint, even if the suction pressure is lower
• B. It increases evaporator temperature to prevent freezing
• C. It stops the compressor whenever the suction pressure rises
• D. It maintains a constant liquid level in the receiver

Answer: (A)

The main idea here is maintaining a minimum evaporator pressure. An evaporator pressure regulator keeps the pressure in the evaporator from falling below a preset value, even if the suction pressure drops. This matters because the evaporating temperature is tied to pressure, and if the pressure gets too low, the coil can frost up and heat transfer can suffer. The regulator acts to bypass or regulate flow so the evaporator maintains that minimum pressure, preserving cooling capacity and preventing ice buildup. It isn’t meant to raise the evaporator temperature, nor to shut the compressor for high suction, nor to control liquid level in a receiver.