Chevrolet Silverado 1500 / 2500 / 3500:

Ac compressor always on

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# 1  11/24/2013 1:26 AM

New member
Registered: 11/24/2013
Posts: 1

Ac compressor always on

I have a 1996 silverado 5.7 and my ac compressor still kicks on and off even if the ac and defrost is in off position. What is my problem?



# 2  11/24/2013 3:12 AM

Registered: 11/24/2009
Posts: 1301

Re: Ac compressor always on

If the A/C clutch is cycling then the system seem to be working properly mechanically, but the electrical portion of the system is faulty.

The problem could be an A/C control unit (A/C control head).

The system is cycling so it seems to show the A/C system is good and the A/C relay is doing its job by turning the clutch on and off.

The signal for the A/C relay comes from the control unit. The control unit gets its signal from the ECU showing the signal is coming from the ECU properly. It's the signal from the control unit that seems to have the problem turning off when commanded off.

Use a voltmeter, check terminal #85 at the A/C relay for changes in voltage when the AC button is pressed

The Heater AC Control Unit switches terminal #85 to complete the circuit for the coil in the relay. With AC on from the Control Unit, #85 should have +12V, and #86 is ground for the relay coil. Power to terminal #30 will engage the compressor clutch. Check for power at #87; it is the power for the clutch circuit from the A/C control unit. If current is constant and does not respond to the A/C button then change the A/C control unit.

Let me know if this information is helpful, if not we can continue diagnostics of the A/C clutch circuit.
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