SENSOR-EVAPORATOR TEMPERATURE
DESCRIPTION
The evaporator temperature sensor measures the temperature of the conditioned air downstream of the A/C evaporator. The evaporator temperature sensor is an electrical thermistor (1) mounted on the end of a molded plastic housing (2) that is inserted into the driver side of the HVAC housing near the coldest point of the A/C evaporator. The evaporator temperature sensor is retained in the HVAC housing by two integral retaining tabs (3) and is connected to the vehicle electrical system by use of a wire lead and connector (4) with two terminals.
OPERATION
The evaporator temperature sensor monitors the surface temperature of A/C evaporator and supplies an input signal to the cabin compartment node (CCN). The CCN uses the evaporator temperature sensor input signal to optimize A/C system performance and to protect the A/C system from evaporator freezing. The evaporator temperature sensor will change its internal resistance in response to the temperatures it monitors and is connected to the CCN through sensor ground circuit and a 5-volt reference signal circuit. As the temperature of the A/C evaporator decreases, the internal resistance of the evaporator temperature sensor decreases.
The CCN uses the monitored voltage reading as an indication of evaporator temperature. The CCN is programmed to respond to this input by requesting the powertrain control module (PCM) or the engine control module (ECM) (depending on engine application) to cycle the compressor clutch off and on as necessary to optimize A/C system performance and to protect the A/C system from evaporator freezing (refer to 24 - HEATING & AIR CONDITIONING/PLUMBING/COMPRESSOR-A/C - OPERATION for more information).
The evaporator temperature sensor is diagnosed using a scan tool (refer to 24 - HVAC Electrical Diagnostics for more information).
The evaporator temperature sensor cannot be adjusted or repaired and must be replaced if found inoperative or damaged.
REMOVAL
NOTE: Illustration shown with air distribution housing removed for clarity.
NOTE: It is not necessary to remove and disassemble the HVAC housing to service the evaporator temperature sensor. The evaporator temperature sensor can be removed for service from underneath the instrument panel.
1. Disconnect and isolate the negative battery cable.
2. Reach up under the driver side of the instrument panel and disconnect the electrical connector for the evaporator temperature sensor (1) from the instrument panel wire harness.
3. Using needle nose pliers, disengage the two retaining tabs (3) that secure the evaporator temperature sensor to the HVAC housing (2) by carefully pulling the sensor straight out of the side of the HVAC housing.
4. Route the electrical connector and wire lead of the evaporator temperature sensor out from under the heater core tubes and remove the sensor from the vehicle.
INSTALLATION
NOTE: Illustration shown with air distribution housing removed for clarity.
1. Route the electrical connector and wire lead of the evaporator temperature sensor (1) under the heater core tubes located on the driver side of the HVAC housing (2).
2. Install the evaporator temperature sensor into the driver side of the HVAC housing. Make sure the retaining tabs (3) are fully engaged to the housing.
3. Connect the electrical connector for the evaporator temperature sensor to the instrument panel wire harness.
4. Reconnect the negative battery cable.