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possible electrical A/C issue

jtdt175 on Mon March 30, 2009 4:26 PM User is offlineView users profile

Year: 1992
Make: Chevy
Model: C1500 Silverado
Engine Size: 5.7L
Refrigerant Type: now 134a
Country of Origin: United States

I purchased my ’92 Silverado in Dec. 2008. Since I got it the temperature control display has been blinking “A/C” for 2 minutes after starting, than goes away. From the owner’s manual and the GM service manual I realize this means there is a problem in the A/C system. I figured that it was low on refrigerant since the compressor clutch would never kick on, that and that is what it typically has been in the past with other older vehicles. After buying the retrofit 134a kit, I recovered the stuff that was in it, then proceeded to add the new stuff. The pressure kept rising but the clutch never engaged. I looked through the GM service manual and they suggested to do the obvious…Is there power to the wires i.e. the cycling switch and the clutch positive wire. There was not. I inserted a jumper on the cycling wires figuring this would complete the circuit telling me if the switch was bad or not. With jumping the cycling switch I still had nothing, the clutch never engaged. My next thought was well maybe the internal clutch relay or the pump was shot. So I ran a jumper from the positive post of the battery, to the positive post on the clutch relay itself. Then the clutch kicked in, I sucked in the 134a and everything was working. I also did this to the cycling switch, when I added power the clutch engaged and all worked. This tells me I have an electrical issue and the mechanical stuff should work. I don’t believe that it would be the cycling switch because with it jumped it should engage the clutch of the compressor and it did not, In fact it did nothing with a jumper on the cycling wires. I assume that I have an issue elsewhere that is causing a dead spot in the system or else the cycling switch would have power to it. Does anyone have any ideas or faced similar situation or hell even heard of any stories remotely similar to this? I would really appreciate any help, short of taking it to a mechanic who is going to charge me way more than the truck is worth to get this working again. Thanks.

mk378 on Mon March 30, 2009 5:25 PM User is offline

As indicated on the dashboard display, the computer has put the A/C into "lockout" due to the previous undercharge. It does this to protect the compressor until the system has been serviced. Disconnecting the battery for a while (with the key OFF of course) should clear the code from memory and restore normal operation.

Beware the "death kit". You should retrofit properly, which at the very least means opening the system to change the oil, and replacing the accumulator.

Dougflas on Mon March 30, 2009 6:11 PM User is offline

There is a modification for that vehicle involving the cutting of a green lead ( at the control head and taping it up. It prevents the falsing of the low freon indication. I thought it was in the tips forum but can't find it right now.I think)

Chick on Mon March 30, 2009 6:52 PM User is offlineView users profile

Your problem could be in the control head, as stated there is a fix, but should not be considered a cure all. You would need to check the refrigerant charge after doing the "mod' to be sure it isn't low ion refrigerant. GM tech wrote a nice article and diagram for it. It is copywrite, so I cannot post it without his permission, so give it a little time til he shows up.. Then we'll get the information to you..Hope this helps..

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

jtdt175 on Mon March 30, 2009 10:36 PM User is offlineView users profile

OK thanks guys, I will give the battery disconnect a shot, and if that doesn't work I will have to move to the mod on the control unit or possibly replacing it all together.

GM Tech on Tue March 31, 2009 8:46 AM User is offline

Sorry- been on a plane for last few hours- just got back from Brazil...

Here is the link you speak of

C/K Truck - 91-92 TSB control head a/c lite flashing

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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......

NickD on Tue March 31, 2009 11:37 AM User is offline

Seems like a weird circuit, the control knows when it is calling for AC, more than likely the mode switch is in one of the AC positions that grounds the relay for what is shown to apply 12 volts to the LPCO switch, where if the system has a charge, it should be closed applying 12 volts to the compressor coil.

Since the control head knows it is applying 12 volts, seems it would expect the compressor clutch coil to also have 12 volts if the cycling switch is closed. But the cycling switch never stays closed, it is constantly switching between ground and 12 volts and that is the input to the control head. Stumps me why a permanent ground to the control head is a fix, is that control head circuit complicated? Would be sure interesting to see the inside of it, maybe then, it would make sense.

S-10 just applied 12 Volts constant to the cycling switch in any of the AC modes, cycling switch took care of the protection and the cycling. If pressure was lost, compressor would never kick on. We all seen that.

GM Tech on Tue March 31, 2009 3:33 PM User is offline

The control head counts cycles to time ratio-- too many cycles too quick and the code is set.....

-------------------------
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......

jtdt175 on Tue March 31, 2009 3:46 PM User is offlineView users profile

Thanks GM Tech, I will be home this weekend to work on the truck I will start with the battery and go from there. Thanks alot everyone. I will let you know if it solves the problem or not. It doesn't make much sense to me either why they wired these trucks the way they did. I am much more familiar with the S10's and older Camaro's systems, they were straightforward. But, as long as it works, is all I am really worried about.

NickD on Tue March 31, 2009 4:21 PM User is offline

Quote
The control head counts cycles to time ratio-- too many cycles too quick and the code is set.....

Makes sense, was next to a truck at a traffic light where his compressor was cycling every two seconds, he needed one of those. Wonder where the trip point is at for the time delay between cycles, could that be the OP's problem? With cool conditions, I like at least 45 seconds, poor check valves would cause that problem as well, but I guess I don't need a blinking light to tell me it's less than that.

NickD on Wed April 01, 2009 5:40 AM User is offline

Bet that cycling switch contacts are starting to chatter as they have the full inductive load of the clutch coil to switch, that would generate extra pulses to fool the computer.

jtdt175 on Fri April 03, 2009 7:46 PM User is offlineView users profile

Ok today I disconnected the battery waited a few minutes and re-hooked it up. The AC blinking light went away and the compressor clutch kicked in and I was able to charge the system. Every thing works great. Thanks guys.

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