Pinpoint Test N : The A/C Is Always On - A/C Mode Always Commanded On: Notes

Diagnostic Overview 

Refer to Automatic Climate Control System for schematic and connector information.

Normal Operation and Fault Conditions 

Voltage is provided to the A/C clutch relay coil and switch contacts. When A/C is requested and all conditions allow, a ground is provided to the A/C clutch relay coil from the PCM, energizing the A/C clutch relay. When the PCM energizes the relay, voltage is supplied to the A/C compressor clutch field coil from the relay. Ground is supplied for the A/C compressor clutch field coil.

An accurate evaporator temperature is critical for compressor engagement and the PCM uses the temperature measurement to turn the A/C compressor off before the evaporator temperatures are cold enough to freeze the condensation on the evaporator core.

When an A/C request is received by the PCM, the A/C compressor clutch only engages through the A/C clutch relay if all of the following conditions are met:

• The HVAC control module does not detect an evaporator temperature below approximately 1 °C (33.8 °F).
• The PCM does not detect excessively high or low refrigerant pressure from the A/C pressure transducer.
• The PCM does not detect excessively high engine coolant temperature.
• The PCM does not detect an ambient air temperature below approximately 0 °C (32 °F).
• The PCM does not detect a temperature sensor reading that does not correlate with the other temperature sensor readings.
• The PCM has not detected a WOT condition.

DTC Fault Trigger Conditions 

Possible Sources 

• Wiring, terminals or connectors
• FCIM
• PCM
• HVAC control module

Visual Inspection and Diagnostic Pre-checks 

• Inspect loose or corroded PCM or HVAC control module connections.