Auto A/C Terms - Glossary
Low Pressure Cut Out Switch

An electrical switch that is wired into the clutch circuit of the A/C compressor, the low pressure cut out switch will sense refrigerant pressures and disengage the A/C compressor, or prevent it from engaging whenever pressures drop below a preset point.

Designed as a safety device to help protect the compressor from catastrophic failure, the low pressure cut out switch typically senses pressures on the low side of the system. In some cases, the compressor cycling switch that controls compressor cycling works as a low pressure cut out as well.

Understand that in an auto A/C system, the refrigerant that is in the evaporator and cools the passenger compartment also provides cooling for the compressor. When refrigerant pressures are low, the A/C system encounters a superheat condition and cooling performance is lost.

When that happens, not only does the passenger compartment loose cooling, the A/C compressor cooling is lost too. Continued operation of the compressor could lead to a catastrophic failure.

It’s also important to note that A/C compressors no longer include any storage or sump for oil. All lubrication for the compressor is supplied in a mist that is carried by the refrigerant. Therefore, when refrigerant pressures drop, not only is compressor cooling lost but compressor lubrication could be lost too.