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 measuring current draw. Begin testing of a suspected compressor clutch coil problem by performing the preliminary checks.

PRELIMINARY CHECKS
1. Perform the Heating and A/C System Self Diagnostics. If no diagnostic trouble codes (DTCs) are found in the body control module (BCM) or the powertrain control module (PCM), go to Step 2. If any DTCs are found, repair as required, then proceed to Step 2.
2. If the A/C compressor clutch still will not engage, verify the refrigerant charge level. If the refrigerant charge level is OK, go to Step 3. If the refrigerant charge level is not OK, adjust the refrigerant charge as required, then proceed to Step 3.
3. If the A/C compressor clutch still will not engage, verify the BCM is receiving and sending an A/C request signal. If OK, go to COIL CURRENT DRAW TEST. If not OK, repair as required.

COIL CURRENT DRAW TEST
1. Verify the battery state of charge.
2. Connect an ammeter (0 to 10 ampere scale selected) in series with the clutch coil feed terminal. Connect a voltmeter (0 to 20 volt scale selected) to measure voltage across the battery and the clutch coil.
3. With the heater-A/C control in the A/C mode and the blower at low speed, start the engine and allow it to run at a normal idle speed.
4. The A/C compressor clutch should engage immediately, and the clutch coil supply voltage should be within two volts of the battery voltage. If the coil supply voltage is OK, go to Step 5. If the coil supply voltage is not within two volts of battery voltage, test the clutch coil feed circuit for excessive voltage drop and repair as necessary.

A/C Clutch Coil Specifications:

5. Refer to the A/C Clutch Coil Specifications chart for the acceptable A/C clutch 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 compressor 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.