COMPRESSOR CLUTCH CIRCUIT DIAGNOSIS
Check System Operation
Ensure ambient temperature is greater than 50 F (10 C). Ensure battery voltage is greater than 12.5 volts. Start engine. Turn blower motor and A/C system on. If compressor clutch engages, circuit is operating properly. If compressor clutch does not engage, go to next step.
Check For Voltage
Check for voltage at A/C pressure switch. If 10 volts or greater exists, go to next step. If less than 10 volts exists, go to step 10).
By-Pass Clutch Cycling Pressure Switch
Disconnect clutch cycling pressure switch (located on accumulator-drier). Ensure engine is running and A/C control panel is set to maximum cooling position. Connect jumper wire across switch harness connector terminals. If the clutch engages, go to next step. If the clutch does not engage, go to step 7).
Check A/C High Pressure Cut-Off Switch
Using an ohmmeter, check for continuity between A/C high pressure cut-off switch terminals. If continuity exists, go to next step. If continuity does not exist, replace A/C high pressure cut-off switch and return to step 1).
Check Refrigerant Pressure
Connect manifold gauge set and note pressure readings. If pressure reading is less than 55 psi (3.9 kg/cm2 ), check system for leaks and repair as required. After repairs, verify A/C system operation. If pressure reading is greater than 55 psi (3.9 kg/cm2 ), replace clutch cycling pressure switch and verify A/C system operation.
Check A/C Compressor Pressure Relief Valve
Inspect area surrounding A/C compressor pressure relief valve for signs of oily residue, indicating relief valve leakage. If oily residue exists, replace relief valve and return to step 1). If oily residue does not exist, inspect refrigerant system for leaks elsewhere and repair as necessary. Recharge system.
Check Voltage At A/C Compressor Clutch Coil
Check for voltage at A/C compressor clutch coil connector. If 10 volts or greater exists, go to next step. If voltage is not 10 volts or greater, go tostep 9).
Check Clutch Coil Ground
Connect jumper wire between ground terminal of A/C compressor clutch coil and ground. If clutch engages, repair open in ground wire. If clutch does not engage, replace A/C compressor clutch coil and return to step 1).
Check fuse for continuity. If continuity exists, go to next step. If continuity does not exist, check for short or blown fuse. Repair as necessary.
Check A/C Control Switch
Ensure ignition switch is in RUN position and A/C system is in defrost position. Check for battery voltage at connector of A/C cycling switch. If battery voltage does not exist, go to next step. If battery voltage exists, go to step 12).
Check A/C Control Switch Circuit
Remove connector from A/C control switch. If 10 volts or greater exists at circuit, go to next step. If voltage is less than 10 volts, check for blown fuse or open White/Purple (Brown/White wire on Bronco). Repair as necessary and return to step 1).
Check Function Switch
Ensure function switch is in defrost position. Check A/C control switch and function switch for continuity. If there is continuity through function switch only, replace A/C control switch. If there is continuity through A/C control switch only, replace function switch. If there is continuity through both switches, repair open circuit between A/C control switch and clutch cycling pressure switch. Go to step 1).
Tuesday, April 28th, 2009 AT 3:16 PM