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Home >> GMC >> 1987 >> Forward Control 4.8 T, Standard >> Repair and Diagnosis >> Engine Performance >> System >> CCC TBI Tests W/Codes >> Diagnostic Charts >> A/C Clutch Control Diagnosis (2.8L) >> Test Description

Test Description

NOTE: Test numbers refer to test numbers on diagnostic chart.
  1. Checks for low refrigerant as cause for no A/C.
  2. This and following tests check for faulty A/C control relay.
  3. Checks for faulty cycling switch. Solenoids and relays are turned on and off by the ECM, using internal electronic switches (drivers). Each driver is part of a group of 4, called "Quad-Drivers". Failure of one driver can damage any other driver in set. Solenoid and relay coil resistance must measure more than 20 ohms. Less resistance will cause early failure of ECM driver. Using an ohmmeter, check coil resistance of A/C relay before replacing ECM.
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