Compressor Clutch Coil: Testing and Inspection

A/C CLUTCH COIL

The A/C clutch coil electrical circuit is controlled by the Powertrain Control Module (PCM) or the Engine Control Module (ECM), depending on engine application, through the A/C clutch relay. The A/C clutch coil can be tested by either measuring A/C clutch coil resistance or current draw. Begin testing of a suspected A/C clutch coil problem by performing the preliminary checks.

PRELIMINARY CHECKS

1. If the A/C clutch will not engage, check for Diagnostic Trouble Codes (DTCs) in the A/C-heater control, Cabin Compartment Node (CCN) or the PCM/ECM. If no DTCs are found, go to 2. If any DTCs are found, repair as required.
2. If the A/C clutch still will not engage, verify the refrigerant charge level by conducting the A/C Performance Test A/C Performance. If the refrigerant charge is OK, go to COIL RESISTANCE TEST and/or COIL CURRENT DRAW TEST. If the refrigerant charge is not OK, adjust the refrigerant charge as required.

COIL RESISTANCE TEST

1. Disconnect and isolate the negative battery cable.
2. Disconnect the wire harness connector from the A/C clutch coil connector.
3. Use an ohmmeter and Back Probe Tool 6801 and measure the resistance of the A/C clutch coil at the coil connector terminals.
4. See the A/C Clutch Coil Specifications chart for the acceptable A/C clutch coil resistance. Specifications apply for a work area temperature of 25° C (77° F).
a. If the A/C clutch coil reading is below specifications, the coil is shorted and must be replaced.
b. If the A/C clutch coil reading is above specifications, the coil is open and must be replaced.

COIL CURRENT DRAW TEST

1. Verify the battery state of charge Battery.
2. Connect an ammeter (0 to 10 ampere scale selected) in series with the A/C clutch coil feed terminal using Back Probe Tool 6801. Connect a voltmeter (0 to 20 volt scale selected) to measure voltage across the battery and the A/C clutch coil.
3. With the A/C-heater control in the A/C mode and the blower motor at low speed, start the engine and allow it to run at a normal idle speed.
4. The A/C clutch should engage immediately and the clutch coil supply voltage should be within two volts of the battery voltage. If the A/C clutch coil supply voltage is OK, go to 5. If the A/C clutch coil supply voltage is not within two volts of battery voltage, test the A/C clutch coil feed circuit for excessive voltage drop and repair as necessary.
5. See the A/C Clutch Coil Specifications chart for the acceptable A/C clutch coil current draw. Specifications apply for a work area temperature of 25° C (77° F). If voltage is more than 12.5 volts, add electrical loads by turning on electrical accessories until voltage reads below 12.5 volts.
a. If the A/C clutch coil current reading is zero, the coil is open and must be replaced.
b. If the A/C clutch coil current reading is above specifications, the coil is shorted and must be replaced.
A/C CLUTCH COIL SPECIFICATIONS