The HVAC Scan Tool Data Definitions contains a brief description of all HVAC related parameters available on the scan tool. The list is in alphabetical order. A given parameter may appear in any one of the data lists. In some cases, the parameter may appear more than once or in more than one data list in order to group certain related parameters together.

PCM -- A/C Relay Command: The scan tool displays On or Off. On is displayed when the PCM has energized the A/C compressor clutch relay.

PCM -- Engine Data 2 -- A/C Clutch Feedback Signal: The scan tool displays Relay On or Relay Off. Represents the state of the A/C compressor clutch as seen by the PCM via the A/C compressor clutch feedback circuit.

PCM -- Engine Data 2 -- A/C High Side Pressure: The scan tool displays 0-3116 kPa/ 0-452 psi/ 0-5 Volts. This parameter represents the A/C refrigerant pressure sensor signal. The amount of pressure indicates the amount of load that the A/C compressor is placing on the engine. The powertrain control module (PCM) uses this information to adjust idle and to control the cooling fans.

PCM -- Engine Data 2 -- A/C Off For WOT: The scan tool displays Yes or No. A/C OFF for wide open throttle (WOT) is indicated if A/C operation has been disabled due to a WOT condition.

PCM -- Engine Data 2 -- A/C Pressure Disable: The scan tool displays Yes or No. Yes indicates that the powertrain control module (PCM) is monitoring an A/C refrigerant pressure signal voltage which is too high, system pressure exceeds 2968 kPa (430 psi), or too low to allow the A/C compressor clutch to engage.

PCM -- Engine Data 2 -- A/C Request Signal: The scan tool displays Yes or No. This parameter indicates the state of the A/C request input circuit from the heating, ventilation, and air conditioning (HVAC) controls. The powertrain control module (PCM) uses the A/C request signal to determine if A/C compressor operation is being requested by the HVAC control assembly.

PCM -- Output Driver Data -- A/C Relay Circuit Status: The scan tool displays OK or Fault. Fault is displayed when an open or short is detected in the A/C compressor clutch relay ground circuit.

PCM-ECT Sensor: The engine coolant temperature (ECT) sensor is mounted in the coolant stream. The scan tool displays a range of -40 to +151°C (-40 to +304°F). The powertrain control module (PCM) applies 5.0 volts to the ECT sensor circuit. The sensor is a thermistor which changes internal resistance as the engine temperature changes. When the sensor is cold, internal resistance is high, the PCM senses a high signal voltage and interprets the voltage as a cold engine. As the sensor warms, internal resistance decreases, the voltage signal decreases, and the PCM interprets the lower voltage as a warm engine.