This is the Hurricane's adjustable thermostatic control, which is located on the right-hand side of the unit. The thermocouple (also called a capillary tube) is inserted into the evaporator to measure box temperature. When the temperature rises to a given value, this thermostatic switch closes, completing the circuit to the compressor clutch. When the evaporator gets cold, the switch opens, disengaging the compressor clutch. Compressor clutch engagement happens only when the fan and micro switches are on and the in-line pressure switch is closed. Three switches need to be closed for compressor operation.