Low Refrigerant Detection System

System is comprised of a superheat switch and thermal fuse designed to protect the compressor against damage when the refrigerant charge is partially or totally lost. The thermal fuse is located on the top of the evaporator case near the ambient sensor and the superheat switch is located in the rear head of the compressor. The fuse is connected in series with the ambient switch and the compressor (see Figure ).

Normally, current flows through the control panel switch, thermal fuse and ambient switch to the compressor clutch coil. If a loss of refrigerant occurs in the system, the contacts in the superheat switch close, as the switch senses low system pressure and high suction gas temperature. When the contacts close, the superheat switch becomes the ground side of a circuit through a heater resistance in the thermal fuse. The resultant heat melts the fuse link and the circuit to the compressor clutch coil is opened. Compressor operation stops and damage due to loss of refrigerant is prevented. The thermal switch unit is not repairable and must be replaced if blown fuse occurs.