For 1990-2009 cars

The HVAC Scan Tool Data Definitions contain a brief description of all the scan tool parameters. This list is in alphanumeric order.

A/C High Side Pressure : The scan tool displays -103 to +3119 kPa (-14 to +452 psi). This parameter represents the A/C refrigerant pressure sensor voltage signal converted to pressure.
A/C High Side Pressure Sensor: The scan tool displays 0.00-5.00 Volts. This parameter represents the A/C refrigerant pressure sensor signal.
A/C Request: The scan tool displays Yes or No. The PCM uses the A/C request signal in order to determine if A/C compressor operation is being requested by the HVAC control module.
A/C Relay Circuit Short to Volts: The scan tool displays Yes or No. Yes is displayed if the A/C relay control circuit is shorted to voltage.
A/C Relay Circuit Open or Short to Ground: The scan tool displays Yes or No. Yes is displayed if the A/C relay control circuit is open or shorted to ground.
A/C Relay Command: The scan tool displays On or Off. Represents the PCM commanded state of the A/C compressor clutch relay. The A/C compressor clutch should be engaged when Commanded A/C displays On.
Auto Switch - Actual: The scan tool displays High or Low. When the AUTO button is pressed the scan tool displays High. When released, the scan tool displays Low.
Auto Switch Command: The scan tool displays On or Off. On is displayed when the HVAC control module is in Auto Mode.
Defrost Switch - Actual: The scan tool displays High or Low. When the Defrost button is pressed the scan tool displays High. When released, the scan tool displays Low.
Defrost Switch Command: The scan tool displays On or Off. On is displayed when the Defrost is selected.
Defrost LED: The scan tool displays On or Off. The state of the Defrost LED.
Economy Switch - Actual: The scan tool displays High or Low. When the Economy button is pressed the scan tool displays High. When released, the scan tool displays Low.
Economy Switch Command: The scan tool displays On or Off. On is displayed when the Economy is selected.
Fan Speed: This data indicates the blower motor speed value as a Counts.
Mix Feedback: This data indicates the actual air mix door position.
Mode Switch - Actual: The scan tool displays High or Low. When the Mode button is pressed the scan tool displays High. When released, the scan tool displays Low.
Mode Switch Command: The scan tool displays On or Off. On is displayed when the a Mode is selected.
Mode Feedback: This data indicates the actual air Mode door position.
Off Switch - Actual: The scan tool displays High or Low. When the Off button is pressed the scan tool displays High. When released, the scan tool displays Low.
Off Switch Command: The scan tool displays On or Off. On is displayed when the Off is selected.
Outside Air Temperature: The scan tool displays 0 to 255 counts (0 to 5 volts). The status of the sensor signal circuit is monitored. 0 counts indicates a short to ground, 255 counts indicates an open circuit.
Passenger Compartment Temperature: The scan tool displays 0 to 255 counts (0 to 5 volts). The status of the sensor signal circuit is monitored. 0 counts indicates a short to ground, 255 counts indicates an open circuit.
Rear Defrost Switch - Actual: The scan tool displays High or Low. When the Rear Defrost button is pressed the scan tool displays High. When released, the scan tool displays Low.
Rear Defrost Switch Command: The scan tool displays On or Off. On is displayed when the Rear Defrost is selected.
Rear Defrost Feedback: The scan tool displays High or Low. When the Rear Defrost is On the scan tool displays High.
Recirculation LED: The scan tool displays On or Off. The state of the Recirculation LED.
Recirculation Switch Command: The scan tool displays On or Off. On is displayed when the Recirculation is selected.
Sun Load Sensor: The scan tool displays 0 to 255 counts. The signal output from the Sun Load Sensor.