Evaporator Temperature Sensor / Switch: Description and Operation

Fig.15 Evaporator Temperature Sensor:

Fig.16 Evaporator Temperature Sensor Setpoint:

The evaporator temperature sensor is located at the coldest point on the face of the evaporator.The switch is attached to the evaporator coil with the sensing probe inserted into the coil fins. The evaporator temperature sensor prevents condensate water on the evaporator coil from freezing and obstructing A/C system air flow.

The Body Control Module (BCM) will send a Programmable Communications Interface (PCI) bus message to the Powertrain Control Module (PCM), which will check engine, coolant temperature, and refrigerant pressure temperature before turning ON the A/C Compressor Clutch. Turning ON the A/C Compressor Clutch will allow the system to cool the evaporator. The BCM will send a message to the PCM when the evaporator temperature becomes too cold. The PCM will then turn OFF the A/C Compressor Clutch, before evaporator freeze up occurs. The DRB III scan tool can be used to monitor this operation. The temperature setpoint at which the clutch is turned OFF varies with the outside ambient temperature. The temperature at which the clutch is turned ON is preset to 2 °F above the OFF setpoint mentioned above. Refer to Evaporator Temperature Sensor Setpoint table and for the correct setpoint.