Compressor Clutch Coil: Testing and Inspection

The air conditioning compressor clutch coil electrical circuit is controlled by the ATC control module which is integral to the heater-A/C control. Begin testing of a suspected compressor clutch coil problem by performing the ATC Function Test using the DRBIII(R) scan tool.

PRELIMINARY CHECKS
1. If no diagnostic trouble codes (DTCs) are found in the A/C-heater control or the powertrain control module (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. If the refrigerant charge level is OK, go to TESTS. If the refrigerant charge level is not OK, adjust the refrigerant charge as required.

TESTS
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 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 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.
5. For the acceptable A/C clutch coil current draw specifications refer to specifications. 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 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.