2005 GMC Sierra A/C works great then stops....

[wsgregory]

My 2005 GMC Sierra A/C works great and then stops....if I turn off the engine and re-start it....the A/C will work again...great. When it's working, everything sounds/and operates like normal, clutch engages....e-fans are operable, etc...no strange noises. When it stops working, the A/C compressor does not cycle even with the A/C turned on....also it doesn't appear to be a blend door or actuator issue.

When it first happened about 2 months ago, I took it to the local GMC dealer to ensure that I had the right pressures. They added a little bit of refrigerant...but it was doing the same thing when I drove it home from the dealer.

Since then, I've replaced the A/C relay, all three HVAC relays, the low pressure switch, the blower motor resistor, and the HVAC control head. The only thing that I haven't replaced is the hight pressure switch (which repair sites show as compressor mounted...but mine appears to be inline with a schrader valve).

I've looked at the other posts and have seen similar problems. I did see that Nacho mentioned that there was a procedure to fix the problem....too. Also, saw a Silverado post with similar symptoms....and he found it to be a dirty connector at his compressor....and cleaned it and it worked like normal again.

Any ideas? If someone could tell me about the procedure that Nacho mentioned to correct the situation....or any other ideas...that would be Great. Thanks.

[wsgregory]

Also...forgot to mention that I changed out the engine coolant temperature sensor, too....

[wsgregory]

Sorry forgot to mention the truck specs: its a 2005 GMC Sierra 1500, 5.3L (engine code T), SLE package, extended cab, with auto trans, A/C is manual dual climate control.

[buickwagon]

The first thing I would do is backprobe the compressor electrical connector when the AC is on but acting up. If the compressor is getting 12v but the clutch isn't engaging, then it would seem to be a clutch issue. If the compressor is not getting power, then it's a control issue.

Actually, scratch that. First thing I would do is connect a scan tool and see if the PCM is calling for the compressor to be on when you think it should be on but it isn't. You can also look at the pressure switch outputs as seen by the computer. If all that looks OK, then I would check for power at the compressor.

[wsgregory]

Thanks.

Will check the power to the compressor and clutch air gap. Will keep you posted.

[wsgregory]

Guys, I tried my best to make the A/C stop working last night and this AM....but the outside temperature has been around 60F. I'm thinking the lower outside temp had something to do with making it act up....and stop working. Anyway, it stopped working this AM after driving for about 20 minutes. I popped the hood and tapped the A/C clutch....and it started working again....so I think I found the culprit.

I haven't checked the pressures yet....but if I can get the A/C to run for about 30-40 minutes constant w/o any problem in cooler temps....don't think it's an under or over charge issue. Also, that should negate the need for me to test power to the A/C clutch when it stops working, right?

So, sounds like time to change out the A/C clutch....am I tracking?

[ACProf]

So, sounds like time to change out the A/C clutch....am I tracking?

No, its time to adjust the clutch gap.

[buickwagon]

ACProf has way more experience than I with compressors (or anything AC related for that matter), so listen to him before listening to me. However I think it is still possible you may have an electrical issue -- possibly the connector itself (loose or corroded contacts or a broken conductor inside a wire) or in the windings that form the electromagnet that engages the clutch. I imagine (which is the best I can do because I've never actually disassembled one) that the windings are similar to a solenoid winding and could be damaged or just have a poorly crimped joint.

My first rule of troubleshooting anything is to check the simplest and easiest things first because they don't take much time, effort or money to eliminate and they are usually the problem anyway. Checking the clutch gap sounds pretty easy and is what ACProf said to do, so it's first. Next after that would be jiggling the wires gently with the AC on to see if it has an effect. Third would be to confirm voltages to ensure your tapping wasn't just a coincidence. Next would be to wait for the AC to crap out again, shut it off, disconnect the compressor connector and meter the terminals on the compressor, looking for an open circuit.

[wsgregory]

Thanks for all of the input. I'll check the clutch air gap tonight and if it's too close....then I should be able to pull off the clutch plate and a shim (washer) behind it to increase the gap, right?

[wsgregory]

Guys, checked the clutch air gap...and I've got .026-.030 all day there. Also, jacked it up and disconnected the clutch wiring plug...and it was totally clean...no corrosion. I plugged everthing back together and started it up with the A/C running and gently moved all of the wires around and it didn't interupt the A/C operation.

Having said that, I live on a hill...and had the truck in the back of the lot on a flat surface while working on it. As I drove down hill afterwards to the driveway...it stopped working....then I turned around and parked uphill in the driveway and the clutch then decide to engage....to me it's almost like gravity helped it along in that case....engaging at a downward angle toward the fire wall.

So....clutch time? Or take off the clutch plate and add a shim? I think I'm at or beyond the max air gap already, right?

[GM Tech]

Just the opposite, take off the clutch driver and REMOVE a shim-- your air gap is too wide to pull it in after the ckutch warms up---it can pull in cold, just not once it gets warm-- if hitting a bump on road, or tapping on it will make it engage- the remove a shim--just so long as clutch does not drag when NOT engaged.

[buickwagon]

The magnet has to pull the clutch in. If it's too far away (big gap) the magnetic force may not be strong enough. Pointing uphill, gravity helps. You say your gap is within the 20-30 thou range, so it should be close enough for the magnetic force to pull it in all the way, but maybe closer to the 20 thou mark would ensure that. Low voltage would reduce the magnetic force. I would meter the voltage to the coil to verify full battery voltage is reaching it -- corrosion elsewhere could affect the voltage available to the clutch. Also, a short-circuit partway through the coil windings will reduce the magnetic force.

Edit: I see GM Tech posted while I was typing. I didn't even think of the heat expansion possibility.

[wsgregory]

Thanks, guys. Good input. Will try pulling a shim tonight...to reduce the gap. Will keep you posted. Thanks to Nacho, too, for the replacement diagram....if it comes to clutch swap time.

[wsgregory]

Ok...I pulled off the clutch plate last night....and for some reason one side of the clutch plate has been grinding when engaged....b/c one side had been ground down a bit and the other was slightly rusty....also there was metal shavings/grease (from the clutch plate) lumped up around the snap ring for the bearing/hub assembly.

I cleaned up the clutch plate and wired brushed the rusty side....and cleaned the metal shavings off of the bearing/hub side.

I ran the A/C today....and it didn't turn off any. I think I'm going to swap the clutch out tomorrow....b/c I'm concerned about the one sided grinding that is apparently taking place....

Could it be that there are two sides to the coil and only one side is engaging as it should? That would make sense....but I haven't looked at an A/C clutch coil before.

[wsgregory]

Changed out the clutch last night....the hardest part was getting the snap rings off....and the new snap rings on....had to use a mirror to get them in/out....b/c of the way the compressor is situated on the truck.

I used a shim that was smaller than the one from the original clutch, too.

All appears to be functioning properly, now. Thanks for the help!