D21 Hardbody 4WD V6-2960cc 3.0L SOHC MFI (VG30E) (1991)
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)