Control Module HVAC: Description and Operation

The thermo control amp located on top of the A/C evaporator housing, provides the ECU with temperature readings of the A/C evaporator. This temperature signal is used by the ECU for A/C compressor clutch on/off control.

The thermo control amp uses a thermistor that is placed on the A/C evaporator. The thermistor changes its resistance as the temperature changes. The resistance change is monitored by the ECU. The ECU then decides if the the A/C compressor will stay on, or be turned off.

The ECU will turn the compressor "ON" when the evaporator temperature is above 37 - 38° F (2.5 - 3.5° C)

The ECU will turn the compressor "OFF" when the evaporator temperature is below 32 - 34° F (0.1 - 0.9° C)