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Electronic Control Module (ECM) Compressor Control Test

  1. Ensure ignition is off. Disconnect ECM 24-pin connectors. Disconnect A/C compressor relay and A/C control relay connectors. Connect a fused jumper wire between Red/Yellow and Yellow wires of A/C compressor relay. Turn ignition switch to RUN (leave engine off).
  2. Set air control knob to NORMAL. For proper test results, temperature outside of vehicle must be 60°F (16°C) or more. Using a DVOM, measure voltage between Brown wire of ECM and ground. Measure voltage between Blue wire of ECM and ground.
  3. Battery voltage should be present at both locations. If battery voltage exists, go to next step. If battery voltage does not exist, check Blue and Brown wires for open circuit. If circuits are okay, replace A/C compressor relay.
  4. Connect a fused jumper wire between Blue wire of ECM connector and ground. With fused jumper wire connected, A/C compressor relay should operate and A/C compressor clutch should engage.
  5. If relay does not operate and compressor clutch does not engage, replace A/C compressor relay. If relay and compressor clutch operate properly, but A/C system still malfunctions, problem may be caused by faulty ECM.
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