Compressor Clutch: Testing and Inspection

A/C COMPRESSOR CLUTCH COIL

The A/C compressor clutch coil electrical circuit is controlled by the powertrain control module (PCM) through the A/C clutch relay. The A/C clutch coil can be tested by either measuring clutch field coil resistance or by measuring current draw. Begin testing of a suspected compressor clutch coil problem by performing the preliminary checks.

PRELIMINARY CHECKS

1. If the A/C compressor clutch will not engage, perform the A/C System Performance Test, which is found within the HVAC System Test. If no diagnostic trouble codes (DTCs) are found in the A/C-heater control or the PCM, go to STEP 2. If any DTCs are found, repair as required.
2. If the A/C compressor clutch still will not engage, verify the refrigerant charge level Refrigerant System Leaks. If the refrigerant charge level is OK, go to COIL RESISTANCE TEST and/or COIL CURRENT DRAW TEST. If the refrigerant charge level is not OK, adjust the refrigerant charge as required.
COIL RESISTANCE TEST

3. Disconnect and isolate the negative battery cable.
4. Disconnect the wire harness connector from the A/C clutch field coil connector.
5. Use an ohm meter and measure the resistance of the clutch field coil at the field coil connector terminals.
6. Refer to the A/C Clutch Field Coil Specifications chart for the acceptable A/C clutch coil resistance. Specifications apply for a work area temperature of 21° C (70° 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

7. Verify the battery state of charge Battery.
8. Connect an ammeter (0 to 10 ampere scale selected) in series with the clutch field coil feed terminal. Connect a voltmeter (0 to 20 volt scale selected) to measure voltage across the battery and the clutch coil.
9. 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.
10. The A/C clutch should engage immediately, and the clutch field coil supply voltage should be within two volts of the battery voltage. If the field coil supply voltage is OK, go to STEP 5. If the field coil supply voltage is not within two volts of battery voltage, test the clutch field coil feed circuit for excessive voltage drop and repair as necessary.
11. Refer to the A/C Clutch Field Coil Specifications chart for the acceptable A/C clutch field coil current draw. Specifications apply for a work area temperature of 21° C (70° 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 field coil current reading is zero, the coil is open and must be replaced.
b. If the A/C clutch field coil current reading is above specifications, the coil is shorted and must be replaced.