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

Diagnostic Overview 

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

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 deg.C (33.8 deg.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 deg.C (32 deg.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.