Temperature Sensor Input

A/C Pressure Sensor

An electronic A/C pressure switch is mounted on the discharge line (high side) of the A/C compressor suction/discharge hose assembly. Its output to the PCM is variable and is dependent upon pressure inside the line.

This sensor operates like other 3-wire sensors. The PCM applies a 5.0 volt reference and a ground for the sensor. Changes in the A/C refrigerant pressure will cause the A/C pressure sensor input to the PCM to vary. The PCM monitors the A/C refrigerant pressure signal circuit and can determine when the signal is outside of the range of the sensor. When the signal is out of range (high or low) for a period of time, the Body Control Module (SBM) will set DTC B1324.

The PCM communicates the status of the A/C system pressure to the body control module (SBM) via Class 2 serial data. A higher pressure results in a higher voltage output. The PCM monitors the A/C pressure to:

^ Disengage the A/C clutch if the pressures are high -2968 kPa (430 psi).
^ Disengage the A/C clutch if pressures are too low -below 255 kPa (37 psi).

In-Vehicle Temperature Sensor

The in-vehicle temperature sensor is a temperature-sensitive resistor like the outside temperature sensor. As outside air temperature increases, resistance decreases. As outside air temperature decreases, resistance increases.

A hose connected to the in-vehicle air temperature sensor continually draws passenger compartment air over the sensor, increasing the accuracy of the temperature reading.

The HVAC programmer monitors the in-vehicle temperature signal and uses this information to help determine command signals.

Heater and A/C Temperature Sensors

The heater and A/C temperature sensors are used to monitor discharge temperatures from the heater and A/C outlets. These sensors are located in the left and right heater and A/C ducts. The HVAC programmer monitors the discharge temperature sensors, and uses this information to help determine command signals.

Outside Temperature Sensor

The outside temperature sensor is a temperature-sensitive resistor whose resistance varies inversely with temperature. As outside air temperature increases, resistance decreases. As outside air temperature decreases, resistance increases.

The HVAC programmer monitors the outside temperature signal and uses this information to display outside temperature on the heater and A/C control VF display and helps determine command signals.

The outside temperature sensor value can be updated by pressing the "OFF," "AUTO" and "VENT" buttons on the Heater and A/C control assembly at the same time. This function will update outside temperature sensor to the current temperature reading.

Solar Sensors

A solar sensor is a light-sensitive photo-diode that monitors the heat load of the sun on the vehicle. The sensors are located on top of the instrument panel, on either side of the defroster grill where sunlight can reach the sensors.

As sunlight intensity increases, the resistance of the sensor decreases. As sunlight intensity decreases, the resistance increases.

The HVAC programmer compares the solar sensor reading to the in-vehicle temperature reading and then determines how much cooling is required to reach and maintain the desired "SET" temperature.