A/C Clutch Control Circuit Diagnosis

A/C Clutch Control Circuit Diagnosis











Circuit Description
When air conditioning and blower fan are selected, and if the system has a sufficient refrigerant charge, a 12-volt signal is supplied to the A/C request input of the powertrain control module (PCM). The A/C request signal may be temporarily canceled during system operation by the electronic thermostat in the evaporator case. The electronic thermostat may intermittently remove the control circuit ground for the A/C thermostat relay to prevent the evaporator from forming ice. When the A/C request signal is received by the PCM, the PCM supplies a ground from the compressor clutch relay if the engine operating conditions are within acceptable ranges. With the A/C compressor relay energized, battery voltage is supplied to the compressor clutch coil.

The PCM will enable the compressor clutch to engage whenever NC has been selected with the engine running, unless any of the following conditions are present:
- The throttle is greater than 90%.
- The ignition voltage is below 10.5 volts.
- The engine speed is greater than 4500 RPM for 5 seconds or 5400 RPM.
- The engine coolant temperature (ECT) is greater than 125°C (257°F).
- The intake air temperature (IAT) is less than 5°C (41°F).
- The power steering pressure switch signals a cramped position.

Diagnostic Aids
To diagnose an intermittent fault, check for the following conditions:
- Poor connection at the PCM - Inspect harness connections for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal-to-wire connection.
- Damaged harness - Inspect the wiring harness for damage; shorts to Ground, shorts to Battery Voltage, and Open circuits. If the harness appears to be OK, observe the NC clutch while moving connectors and wiring harnesses related to the A/C. A sudden clutch malfunction will indicate the source of the intermittent fault.

A/C Clutch Diagnosis
This chart should be used for diagnosing the electrical portion of the NC compressor clutch circuit. A Scan Tool will be used in diagnosing the system. The Scan Tool has the ability to read the A/C request input to the PCM. The Scan Tool can display when the PCM has commanded the A/C clutch ON. The Scan Tool should have the ability to override the NC request signal and energize the A/C compressor relay.