Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET1999EXPRESS 1/2 TON VAN V6-4.3L VIN WREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSTESTING AND INSPECTIONCOMPONENT TESTS AND GENERAL DIAGNOSTICSA/C COMPRESSOR CONTROL CIRCUIT DIAGNOSIS
1999 Chevrolet Express 1/2 Ton Van V6-4.3L VIN W
A/C Compressor Control Circuit Diagnosis
1999 Chevrolet Express 1/2 Ton Van V6-4.3L VIN WSECTION A/C Compressor Control Circuit Diagnosis
Circuit Description
The VCM control of the A/C clutch improves idle quality and performance by performing the following conditions:
^ Delaying clutch engagement until the idle speed is increased
^ Releasing the clutch when the idle speed is too low
^ Providing additional fuel at the instant the clutch is applied
The additional fuel smooths the cycling of the compressor.
Turning the air conditioning ON supplies battery voltage through the pressure switches to the VCM. When the VCM receives the voltage on the A/C request signal, the A/C enable relay circuit is grounded. The A/C compressor clutch then engages.
Diagnostic Aids
An intermittent may be caused by any of the following conditions:
^ A poor connection
^ Rubbed through wire insulation
^ A broken wire inside the insulation
Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis. Symptom Related Diagnostic Procedures
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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.