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no power to a/c compressor

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# 1  10/25/2017 10:15 PM

New member
Registered: 10/25/2017
Posts: 1

no power to a/c compressor

I have a 2008 1500 Silverado 5.3 engine Z71. My a/c quit. Compressor clutch not engaging. This is what I've been able to determine for sure. Power in and out of low pressure switch. No power to the compressor terminal. No power to the a/c fuse (none in, none out). Power to the a/c relay at two terminals. Continuity between pin terminals opposing crossways on a/c relay. Switched the relay with fog lamp relay and clutch did not engage but fog lights work. My question is where do I go from here? I don't have a schematic. Thanks



# 2  10/26/2017 2:55 PM

Registered: 11/24/2009
Posts: 1306

Re: no power to a/c compressor

The first thing to check is to see if you have enough refrigerant in the system. If the low side is below 22 psi the low pressure switch will not close it must be around 40 psi for the switch to close. When it closes it sends a signal to the PCM to ground the A/C relay closing the circuit for the clutch to operate.

If you jump the terminals at the low pressure switch does the compressor clutch operate?

If you ground the terminal #86 at the relay does the compressor clutch engage?

Does the compressor clutch have a good ground at the compressor?

What is the OHM reading at the clutch coil? It should be around 10 OHM"s.

If you know someone with a scan tool then can check the clutch circuit and check the pressure switches for proper operation and also check to see if there are any codes in the A/C system stored in the computer.

The last resort it could be a faulty A/C control or a faulty PCM. I am sending you a schematic for the clutch circuit, I hope this helps.
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