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A/C system works and sometimes, it don't

idrd on Tue September 01, 2009 11:37 PM User is offline

Purchased everything from Arizona Mobil Air and to be honest, they are great people. Replaced the Evaporator ( I would charge a gazzillion dollars if I had to do that for a living ) Compressor, dryer. Condensor was in great shape and hoses are new. Installed everything and my neighbor has the proper equipment and did whatever you do, drain the system then charged it up. This is in a 1996 blazer 4.3 engine W code 4WD.

Here is the problem. If I leave the switch on for the AC and start the truck up in the morning, the air works great. Usually get a temp of 51 to 53 degrees coming out of the center vents. I can stop at a store, start it up again and all works fine, as long as I do not touch the AC switch on the dash. Here is where it gets weird. If I stop the truck, shut the AC switch off and shut the truck off, when I start it up again and turn the switch on, the compressor does not come on. Does not matter if its on MAX air or the regular air. Fan motor works fine at all speeds.

Now, I leave the switch turned on, compressor does not come on. Drive home, pissssssed because I touched the switch park it and leave the switch in the on position. Get up in AM, start truck, AC works fine. Could this be a switch problem in the dash ? I did use the same pressure switch from the old compressor and have not checked that or the old one I used on the dryer.

I have not tested either switch while it was running after all of this started happening, too friggin hot. I was told though to test the two prong switch, jump it, on the dryer when this happens. Disconnect it and jump the two terminals on that switch and if compressor goes on thats the problem. Is all of this correct ? Want to Thank Everyone again at down there for all their patience and their help.

Dougflas on Wed September 02, 2009 5:51 AM User is offline

Put a test light at the compressor leads. If you have a light, tap the clutch hub while engine iss running. Clutch hub may be experiencing too wide a gap or needs to wear inas the spring tension of the hub is a little too strong.

GM Tech on Wed September 02, 2009 8:23 AM User is offline

Why anyone would ever turn off a/c switch in summer baffles me---some folks think turning off controls first causes less strain on battery when starting vehicle-- but the truck already "knows" this and is designed not to run accessories in the "start" or "crank" positions of the ignition switch-- so fiddling with blower motor or a/c or radio controls only serves to wear out the switches-- has no interaction with starting the vehicle....

Next time it is off and is commanded on- do like mentioned above-- tap on front of compressor hub-- most likely a wide air gap..........which can be adjusted by "borrowing" the adjusting tool from Autozone.

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

idrd on Fri September 04, 2009 8:56 PM User is offline

Thanks, problem solved for now. Did as you said, just leave it on A/C max even when I shut it off. System now works fine, no more compressor not going on. I could assume then to replace the AC switch when the heat from hell is gone and its a little easier to work in garage. Thanks again.

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