An automatic temperature control system for regulating the temperature of a vehicle passenger compartment at an operator selected temperature. The system employs an in-car transducer which senses compartment air temperature and emits a vacuum control signal to a vacuum operated servoactuator. When ambient temperatures require heating, the servoactuator is operative to shut off the cooling refrigerant compressor and modulate the opening of the heater core water valve for controlling the temperature of forced air discharge from the heater core. When ambient temperatures require cooling, the servoactuator closes the heater core water valve and intermittently opens and closes a switch for cycling the refrigerant compressor to modulate the temperature of forced air discharge over the refrigerant heat exchanger. The transducer receives blower discharge air for aspirating in-car for temperature sensing. A minor portion of the blower discharge is diverted to impinge on the temperature sensor for sensing condensate freezing on the refrigerant heat exchanger.