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HOMESERVICE MANUALSGMC1995RALLY G2500, 4.3 ZREPAIR AND DIAGNOSIS (SINGLE PAGE)HEATING, VENTILATION & A/C (HVAC)HVAC CONTROL SYSTEMSHVAC SYSTEM - G SERIES VANTROUBLE SHOOTINGA/C COMPRESSOR INOPERATIVE
1995 GMC Rally G2500, 4.3 Z

A/C Compressor Inoperative

1995 GMC Rally G2500, 4.3 ZSECTION A/C Compressor Inoperative
NOTE: To properly diagnose system, outside temperature must be greater than 60°F (16°C).
  1. Turn ignition switch to RUN position. Place blower switch in HI position. Ensure A/C is on. If blower motor runs, go to step 3). If blower motor does not run, go to next step.
  2. Connect test light from Brown wire at blower switch connector to ground. If test light glows, go to next step. If test light does not glow, repair open Brown wire between blower switch connector and fuse block.
  3. Connect test light from Brown/White wire at mode selector control connector to ground. If test light glows, go to next step. If test light does not glow, check for open Brown/White wire between mode selector control connector and blower switch connector. If wire is okay, replace blower switch.
  4. Connect test light from Light Green wire at evaporator pressure control switch (located on A/C accumulator) to ground. If test light glows, go to step 5) on 7.4L or step 7) on all other models. If test light does not glow, check for open Light Green wire between evaporator pressure control switch connector and mode selector control connector. If wire is okay, replace mode selector control.
  5. Connect test light from Dark Green wire at high pressure cut-off switch connector (located on rear of A/C compressor) to ground. If test light glows, go to next step. If test light does not glow, check for open Dark Green wire between high pressure cut-off switch connector and evaporator pressure control switch connector. If wire is okay, replace evaporator pressure control switch.
  6. Connect test light from Dark Green wire at coolant temperature cut-off switch connector (located on left side of engine, on cylinder head) to ground. If test light glows, go to next step. If test light does not glow, check for open Dark Green wire between coolant temperature cut-off switch connector and high pressure cut-off switch connector. If wire is okay, replace high pressure cut-off switch.
  7. Connect test light from Dark Green wire at A/C compressor connector to ground. If test light glows, go to step 10). If test light does not glow, go to step 9) on 7.4L or step 8) on all other models.
  8. Check for open Dark Green wire between A/C compressor connector and evaporator pressure control switch connector. If wire is okay, replace evaporator pressure control switch.
  9. Check for open Dark Green wire between A/C compressor connector and coolant temperature cut-off switch connector. If wire is okay, replace coolant temperature cut-off switch.
  10. Connect test light between Dark Green wire and Black wire of A/C compressor connector. If test light glows, replace A/C compressor. If test light does not glow, repair open Black wire between A/C compressor and ground.
RENDER: 1.0x

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.