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04 silverado a/c issues


JDC2500HD

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First off let me say how great this site is. Now for my issue. A/C started intermittently blowing warm air on occasion. Air starts out ice cold then goes warm. Might be 5 miles might be 20. Took the truck to a local shop and they told me that the system was low on freon. So they evacuated the system then recharged and added dye to check for leaks. Told me it might last all summer or a couple of weeks. This was on a Saturday. On the following Wednesday same issue, Took truck back to the shop following Saturday. The issue happened at the shop so the mechanic saw what it was doing. He ran some diagnostics and this is what he came up with. Power at the a/c clutch but would not cycle, scan tool shows switch off when it is on on the dash, I believe the high and low pressures were within range. Told me I need a new compressor and it would cost a $1000.00 to fix. My question, is it the compressor or the clutch? Again, it starts out cold then goes warm and may not go cold again for some time even after the truck has been run and shut off several times.

Thanks in advance for any advice. Jeff

 

 

 

 

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If the radiator fans do not come on with the compressor, the high side pressure will get so high it will stall the compressor. That will cause the belt to come off as well. Once compressor stops for a few seconds, it will start up again until pressure stalls it. Running a garden hose over the condenser will prevent the compressor from stalling as well.

 

To the OP, I agree with others in regards to locating another shop for a second opinion. The way you have worded your post I would say you are trying to repeat what they told you, but, you are wording it so it makes sense to you, unfortunately, what makes sense to you does not make sense to others. Can you recall what they exactly said? I don't expect people to understand mechanic "speak", but, they should never walk away not really understanding what it going on. Ask them to explain until you do understand the logic. Does not mean you need to learn how to fix you car, just that you need to have an understanding BEFORE you make a decision.

 

Generally, if the AC stops blowing cold air, it means that the pressures in the system are out of specs. That can be caused by many things. One of the most common thing I ran into over all the years is a plugged fixed oriface tube. That will create a low pressure condition on both sides of the system. Not uncommon for the mechanic blame the compressor for it. About half the time it was the compressor that created the crap that plugged the tube, so replacing the compressor was a correct partial repair. To do it correctly, you need to flush the entire system to remove all the crap, then replace the receiver/dryer, fixed oriface tube, compressor and then vacuum for 30 minutes and recharge. I think a grand for all that is likely not far off. The flush part is not cheap.

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I am also experiencing issues with my gauge cluster. Sometimes when the truck is started none of the gauges will work, only the CEL lights up. Sometimes the cluster will come on after a few seconds or maybe a few minutes. Sometimes when the key is turned on , all the lights will light up and driver 1 will display, other times nothing until the truck is actually started. Is this the cluster, BCM, and does the BCM have anything to do with my a/c issue posted earlier? I have the manual temp controls.

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Common problem these days. Rapping on the compressor with a hammer handle usually makes it engage in those cases, and if the gap is too wide.

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I replaced the A/C belt on my truck put it all back together started the truck and turn the A/C on. I had cold air then all of a sudden I smelt something and heard something let go. I looked under the hood and saw the belt cam off and was all in a knot. No saving it and try to put it back on. Does anyone know why this would have happened? Before I did anything I checked the compressor and I could move it with my hand.

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If everything was fine before and the only thing that happened is you changed the belt I'd bet it was not run back quite the same way. Check your diagram for the belt and make sure the groves on the belt are in the groves of the pulleys.

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Holy crap - I rebuilt an entire system on my '86 Grand Marquis for about $600. New EVERYTHING from grille to cabin. Did it myself, but still!

 

If the scan tool shows the switch is off when it's on, there could be a problem with the HVAC control unit. But, how can the clutch show power when the computer thinks it's off? That doesn't make any sense to me.

 

If there's 12v at the clutch I would disregard the control unit for now - if the ground is also good to the coil, then either the clutch coil is bad, or the clutch gap has worn itself too large. Fixing that is as simple as removing shims ... IF you live outside of the rust belt. Sometimes the shaft and nut get so rusted up, the only solution is to replace the compressor.

 

My advice would be to find another shop, personally. No way on earth a compressor replacement should cost $1,000. I'd expect that sort of ridiculous pricing from a GM dealer.

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Maybe I don't understand how these newer trucks are wired. If the tech is reading A/C parameters on a scan tool on a vehicle with manual HVAC controls, something doesn't make sense to me there.

 

The BCM does normally control all the electronic interior comfort features, along with the anti-theft system. I don't know how it can control an HVAC system with manual controls, however. I would say it doesn't ... but I just don't know for sure.

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