A low pressure cut-off switch is used to...

• A. Shut down on high pressure
• B. Monitor liquid line temperature
• C. Establish a minimum operating pressure in the evaporator
• D. Control compressor speed

Answer: (C)

A low pressure cut‑off switch protects the compressor by preventing the suction pressure in the evaporator from falling below a safe minimum. It constantly monitors the suction (low‑side) pressure and, if that pressure drops to the preset limit, it shuts the compressor off. This ensures there is enough refrigerant in the evaporator to absorb heat and helps prevent damage from oil starvation or overheating when the system is starved of refrigerant. It’s not about liquid line temperature, not a high‑pressure shutdown, and not a speed control device, so it specifically serves to establish and maintain a minimum evaporator pressure.