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A/c Problems

charlieheyn

By charlieheyn
in Ask A GM Technician

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charlieheyn New Member

charlieheyn

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I have a '96 GMC Sierra with a 5.7 Litre. The A/C quit two years ago, and I finally decided I should check out the system. (summer finally hit) There was some pressure in the system, but to check it right, I decided to recover, and vacuum the system so I knew if I had the proper amount. The vacuum held for two hours with no change, so I recharged the system. (two lbs.) The compressor won't kick in, so I had to hot wire it. It will engage when I jump it, so I know the clutch is good. The light is on in the dash, and the heater/ac fuse is good. I am wondering about the switches. I jumped (shorted) the high pressure switch at the compressor, and the low psi switch at the receiver/dryer, and nothing. Are the switches normally open or closed? Is there somewhere else I should be looking other than the switches and/or a bad control circuit to the clutch?

bill190 Enthusiast

bill190

Posted
Posted

My 92 drawings also show an A/C clutch relay. Then the pressure switches as being closed when the pressures are what they should be. So switches closed to operate relay which in turn operates the compressor.

 

Then a fusible link (not a fuse) at battery junction block to some of this in addition to a A/C / Heater fuse.

 

Pretty much need a wiring diagram to troubleshoot this.

txab Senior Enthusiast

txab

Posted
Posted

If you have a 2 wire low pressure cut out, you can jumper that low pressure switch.

charlieheyn New Member

charlieheyn

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So, I pulled the cover off of the relays to check the relay ( I never even thought of a relay for the clutch . . duh )

and I found the the relay had popped out of the connector. That or someone played a really stupid trick on me. I plugged it back in, and my summer woes are over. I guess it just goes to show you, don't assume anything. Thanks guys!!

 

Oh, and about the hotwire question, the A/C clutch is just a twelve volt clutch circuit. You have a battery pretty close to that connector. I just used two jumper wires to the battery, and Voila, the clutch is engaged. Just make sure you have refrigerant and oil in the system, or you just bought yourself a compressor.

bill190 Enthusiast

bill190

Posted
Posted
So, I pulled the cover off of the relays to check the relay ( I never even thought of a relay for the clutch . . duh )

and I found the the relay had popped out of the connector...

 

Well that's a new one on me! The older vehicle relays are pretty much "stuck" to their connectors, so never a problem of a relay coming loose.

 

But anyway you never know where the trouble is, so need to check everything...

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