QuestionQUESTION: The compressor in my 99 Tahoe will not shut off even when the A/C is not in the on position, eventually freezes the lines. I have power to the compressor all the time. Ive switched out A/C relay, pulled the fuse in the cab, even pulled out the head control and left it out started the truck, A/c compressor stays engaged, Any ideas.
ANSWER: Jim,
Interesting. First let me thank you for your specificity. Alot of questions that I get on here are very vague, and hardly any ever let me know what they have already tried. Ok, moving to your wiring diagram now. I am going on the assumption that you have the 5.7L engine rather than the 6.5L. There are a few differences, but none substantial.
First, yes, there is an A/C fuse under the dash. However this is not the one that powers your compressor clutch. The underdash fuse powers your blower motor. Your compressor clutch fuse is located in the underhood fuse-relay box. It is a 10A fuse that feeds the compressor clutch relay through an orange wire. The relay then sends the power to the clutch itself through a green wire after the relay's coil is energized. If you pull this fuse it will disengage the compressor entirely. Does it? If so... good. If not... some one has messed wih the wiring in your truck prior to you owning it maybe, or you have a shorted wire that coontiues to feed the compressor through an alternate source of power. If it disengaged the clutch....
Plug this fuse back in. Now pull the 10A fuse in the underhood box that feeds your a/c clutch relay. This should also disengage the compressor clutch. If it does not... then your compressor clutch relay is faulty, or the wires inside the socket connector are crossed/hooked up backwards.
If your relay checks out as good, and your wiring is all correct, and you do not have a shorted/crossed wire pulling voltage from somewhere else... The next stop I would look at is to check the wire going to your compressor clutch. It should be a green wire. Have you done or had done any work to the engine lately that would require the disconnection of any wiring? Someone may have hooked another hot wire to the compressor, rather than the greenthat is supposed to be there. I don't really see this happening because the compressor plug is usually specific and not interchangeable with any others in the harness.
I hope this was of some help. If I can do anything further, do not hesitate to ask. Thank you for the question, if you found my reply to be satisfactory, please remember to rate this answer. Thank you again and good luck in everything.
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QUESTION: Thanks for the quick response, As far as the relay and fuse box under the hood, once each of them is pulled at different times it does in fact shut off the compressor. I just pulled out the A/C control head disconected the entire unit, Compressor still runs. I then disconected the wires to the compressor itself and it will also shut off. I tested the leads from the Blk/Green wire that plug into the unit, They are always hot except when I pull the fuse or relay under the hood. The engine has not been worked on recently, just started doing this in the last week. Im just at a loss on why the compressor runs all the time and freezes the lines even when the A/C is turned off. Is there a way to check and see if the control head is bad? I was thinking that if I disconected the wires and pulled the unit, the compressor should shut off if the head was bad...not the case its still running and freezing the lines. Thanks again
AnswerJim,
According to the wiring diagram that I have there is no blk/grn wire. There is a black wire and there is a couple green wires. I also see that in your control head itself, when the off mode is selected it routes the power that it receives in on the brown wire to an A/C disable switch also in the control head. But that is as far as it takes me. It doesn't break down the control head itself as far as I would like it to. So, yes, generally I could work through the testing of the head, but in this case, I have nothing to reference to. If you take it to a reputable shop, they should have a more thorough breakdown that what I am looking at. But theoretically, if your a/c disable switch inside the control head is not operating correctly, then it would be doing exactly as described. Even with the head unit taken out of the vehicle the compressor would be still be recieving power through the relay and the VCM would be giving it its ground. So either this disable swithc inside the head unit is faulty or the Vehicle Control Module is thinking it is recieving all the correct signals when it really isn't.
Just though of something. Plug in the head unit. Turn the switch to off, and check the dark green wire connecting the control head terminals from the "D to C3" terminals. This is what is sending power to your A/C disable. You should read power to these terminals. With it off, you should NOT read voltage on the light green wire leading out of the control head that goes to your high pressure switch. Now turn the switch to any position other than off. You should not read voltage on the Dark green and should read voltage on the light green. If you are reading anything other than this, I would think it is safe to say that your control head is faulty. But again, take it to a shop and have them check it. I can only do so much through the computer without looking directly at it.
Thank you for the question again. Hope I was of a bit more assistance this time around. If so, please remember to rate this answer. Thanks again and good luck in everything. Feel free to ask if you are in need of anything further.
