Thermostatic Disc 8022337One New Aftermarket Replacement Thermostatic Switch (Disc) for Hesston, Fits Case International Harvester, Fits John Deere, Fits Massey Ferguson, and More This thermostatic switch also called a thermostatic disc or rotary thermostatic switch is an A C system component used in the cab air conditioning circuits of tractors, combines, and other agricultural equipment. The switch uses a capillary tube to sense evaporator temperature and cycle the A C