Need A/C troubleshooting help
 

I have a '98 Jimmy with an intermittent a/c (auto climate control). I have searched the forum but can't seem to find my exact problem. My a/c cools fine for a couple of minutes then the compressor drops out. I find that if I rev the engine to about 3500rpm then back to idle, the a/c blows cold again, but only for a couple of minutes. I had a mechanic friend evacuate the system and charge it to factory specs but the problem persists. I have cleaned the condensor coil thinking that a dirty coil might cause high pressure cutout. I can bypass the clutch cycling switch on the accumulator and the the system cools fine (which lead me to replace the switch thinking that it was not sensing pressure properly - no help). I don't have any tech data so I'm at a disadvantage. Any suggestions would be appreciated.

RE: Need A/C troubleshooting help
 

Im pretty sure the sensor on the accumulator is a low pressure cut out. Have you checked the pressure in the system since having the system recharged?

RE: Need A/C troubleshooting help
 

The low pressure cut off is on the passenger side of the engine compartment. The high pressure cutoff is located at the back of the compressor. You could verify that you are hitting the high pressure limit by disconnecting the switch and putting a jumper across the pins in the switch. If that is the case, then there is either insufficient cooling in the condenser, a problem with the filter/dryer causing a restriction, or possibly a clog in the orifice tube causing a restriction.

Not knowing the history of the system, I would recommend that you replace the filter/dryer and at least clean the orifice tube.

RE: Need A/C troubleshooting help
 

I had the exact same problem in a Buick Regal years ago. It turned out to be the compressor clutch. The clutch engages when the clutch coil is eneregized which magnetically engages the clutch. You can actually see it pull in; there's a slight gap when the clutch is de-energized. This gap closes when the clutch is engaged. My problem was solved by the dealer who gave the clutch face a very firm tap with a hammer. This apparently reduced the gap and the AC work great after that. The "proper" fix would be to replace the compressor clutch coilwhich is probably weak. The very firm tap in my case reducedthe gap between the clutch which compensated for the weak coil. The reason your compressor engages when you rev to 3500 rpm is because at the higher rpm the alternator will put out a little more voltage; enough for the cluch to engage with the weak coil. Good luck. Hope this helps.

RE: Need A/C troubleshooting help
 

I didn't have time to tinker today. I think I'll try bypassing the hi press cutout switch like swartlkk suggests and see what that does. The thing that bugs me is the fact that revving the engine makes the compressor start again. I thought the higher RPM would result in a slightly higher pressure. If it is cutting out on hi pressure limit, it doesn't make sense that even higher pressure would cause it to start. Maybe I don't understand the system pressures like I think I do. By golly, I think I'll just bypass each cutout switch and see if one clears the symptom. If that doesn't work, I'll whack the clutch with a hammer then change the accumulator and clean the orifice tube. That'll show it!

Thanks a ton for the suggestions. I'll let ya know what the eventual fix is...