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Home >> Lincoln >> 1997 >> Mark VIII Base >> Repair and Diagnosis >> Suspension >> Electronic Suspension >> Suspension - Electronic Air >> Self-Diagnostic Tests >> DTC 75: Compressor Relay Control Circuit >> Air Compressor Operation

Air Compressor Operation

Compressor is energized by air suspension/EVO steering control module through solid state air compressor relay. Compressor is activated when control module grounds Dark Blue/Yellow wire circuit.

NOTE: Air compressor relay, a solid state device, does not respond to established relay testing methods. Air compressor relay can get extremely hot during operation. Use care when handling relay.

  1. Check Relay Connector

    Turn air suspension off. Disconnect compressor relay 4-pin connector, located on compressor assembly. Inspect relay and harness connector terminals for corrosion and damage. Repair connector or replace relay if necessary. If connections are okay, go to next step.

  2. Check For Open Black/Yellow Wire

    Turn air suspension off. Turn ignition on. Disconnect air compressor relay connector. Measure voltage between ground and Black/Yellow wire at relay connector. If battery voltage is present, go to next step. If battery voltage is not present, repair open Black/Yellow wire. Check system operation.

  3. Check Voltage On Dark Blue/Yellow Wire

    Turn air suspension off. Turn ignition on. Measure voltage between ground and Dark Blue/Yellow wire at relay connector. If battery voltage is present, leave voltmeter connected and go to step  8. If battery voltage is not present, go to next step.
  4. If voltage reading from step  3 is zero volts, go to step  6 . If not, go to next step.
  5. If voltage reading from step  3 is between 2 and 10 volts, go to step  7. If not, go to next step.

  6. Check For Short To Ground In Dark Blue/Yellow Wire

    Disconnect control module connector C205 (Gray). See Figure. Measure resistance between ground and Dark Blue/Yellow wire at compressor relay connector. If resistance is less than 10 k/ohms, repair short to ground in Dark Blue/Yellow wire and check system operation. If resistance is greater than 10 k/ohms, repair open Dark Blue/Yellow wire.

  7. Check Ground Circuit

    Measure resistance between ground and Black wire (Gray wire on 1996 models) at compressor relay harness connector. If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, repair open Black wire between ground and compressor relay connector.

  8. Check Dark Blue/Yellow Wire For Short To Battery

    Disconnect control module connector C205. Measure voltage between ground and Dark Blue/Yellow wire at compressor relay connector. If voltage does not exist, go to next step. If voltage exists, locate and repair short to battery in Dark Blue/Yellow wire. Check system operation.

  9. By-Pass Compressor Relay

    Reconnect 4-pin compressor motor connector. Connect a fused (30-amp) jumper wire between Purple/Orange wire and Black/Yellow wire terminals at compressor relay harness connector. Compressor should run when jumper wire is installed. If compressor runs, replace compressor relay. If air compressor does not run, go to DTC 98 , under TESTS.
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