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A/C Clutch Circuit Electrical Diagnosis (CAPRI, Continental, Cougar, Escort, Exp, Lynx, Mustang & THUNDERBIRD Only)

An inoperative A/C compressor clutch may be caused by a diode connected in parallel to clutch field coil. If diode is shorted, symptoms will be the same as a shorted field coil (blown fuse). To prevent unnecessary replacement of clutch field coil, use the following test procedure:

  1. Disconnect wiring harness connector from A/C clutch field coil assembly. Using an ohmmeter, set at a low resistance range and connect test leads across 2 prongs in field coil connector. Ohmmeter should read approximately 2.5 to 4.5 range. If ohmmeter reads less than specified range and indicates a short condition, field coil must be replaced.
  2. If resistance falls within specified range and short condition still exists when wiring harness connector is reconnected, diode and diode wiring harness should be tested for a short condition. Using an ohmmeter, set at a high resistance range and connect test leads across terminals of wire connector.
  3. If resistance falls to zero, reverse leads at connector. If resistance reads in excess of 100,000 ohms, diode is good. If resistance is zero, diode is shorted and must be replaced.
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