Theory Of Operation

The HVAC A/C heater control uses a variety of sensors to adjust HVAC operation to obtain optimal performance. These sensors are continuously monitored by the A/C heater control to assure that they are in range. An active Diagnostic Trouble Code (DTC) indicates that a sensor is out of range. A stored DTC indicates that the sensor was out of range but is currently within range.

The evaporator temperature sensor monitors the surface temperature of the A/C evaporator and supplies an input signal to the A/C heater control. The input signal value is used to optimize the A/C system performance and to protect the A/C evaporator from freezing. The evaporator temperature sensor resistance value will change in response to the surface temperature of A/C evaporator. The resistance value is electronically transferred to the A/C heater control using a sensor ground circuit and a 5-volt reference signal circuit. Normal operation of the sensor the resistive value decreases when the A/C evaporator temperature decreases and the sensor resistive value increases when the A/C evaporator temperature increases.