Which device is used to prevent evaporator pressure from falling below a set limit?

Which device is used to prevent evaporator pressure from falling below a set limit?

• A. Low-pressure cut-off switch
• B. Sight glass
• C. Evaporator pressure regulating valve (EPR)
• D. Thermostatic expansion valve

Answer: (C)

Maintaining a minimum evaporator pressure keeps the refrigerant boiling properly and protects both the compressor and overall cooling performance during light or variable loads. An evaporator pressure regulating valve senses the suction pressure and actively modulates refrigerant flow to the evaporator so the pressure doesn’t drop below a preset limit. When the pressure risks dipping, the valve opens a bit to allow more refrigerant into the evaporator; as pressure rises, it closes again. This direct regulation of suction pressure is what sets it apart from other devices: a low-pressure cut-off switch is a safety shutoff, not a regulator of continuous pressure; a sight glass merely shows charge level; and a thermostatic expansion valve mainly controls flow to meet evaporator superheat, not specifically to hold a minimum evaporator pressure.

Maintaining a minimum evaporator pressure keeps the refrigerant boiling properly and protects both the compressor and overall cooling performance during light or variable loads. An evaporator pressure regulating valve senses the suction pressure and actively modulates refrigerant flow to the evaporator so the pressure doesn’t drop below a preset limit. When the pressure risks dipping, the valve opens a bit to allow more refrigerant into the evaporator; as pressure rises, it closes again. This direct regulation of suction pressure is what sets it apart from other devices: a low-pressure cut-off switch is a safety shutoff, not a regulator of continuous pressure; a sight glass merely shows charge level; and a thermostatic expansion valve mainly controls flow to meet evaporator superheat, not specifically to hold a minimum evaporator pressure.