a/c issues

Hey Guys, I have a 1999 Cherokee Sport with the 4.0L, and I seem to be having some a/c problems. When I first crank the Jeep, and the engine is cool, the a/c works flawelessly. The compressor stays engaged until you turn the system off, which is where my problem begins. I have noticed that when the system is running, the compressor does not cycle off, the fans and the compressor stay engaged until you turn the selector off. After the engine has warmed and you have ran the system for awhile, and turn it off, and then attempt to turn it back on, the fan starts running, but the compressor does not engage. I know that the system is fully charged due to buying a pressure gauge to test the pressure. Any thoughts on the compressor not reengaging after turning the system off? I am wondering if maybe one of the pressure sensors is going bad or is their a compressor cycling switch on this car? Any help or thoughts is greatly appreciated!

I'm pretty sure that the ECM monitors the clutch circuit so it might be a mechanical problem with the clutch itself

I had a similar issue. Mine was it would work for a few cycles then quit. I had to evacuate the whole system and then recharge to spec. I think is 1.25 lbs. and it has worked since. If you dont have the means to evacuate properly. Take it a shop, and have them evacuate and recarge the system. also you can cheack for leaks with a black light and look for a green shine. let me know. if you have your own gauges it should be low/blue side about 30-35psi and red/high about 150psi.

I would like to bump this because I have this same problem. When the engine is cold the a/c clutch engages and everything is fine. I can make a 3 hour trip and its fine. Stop to get gas and turn the jeep off and when I go to crank it back up the clutch wont engage. I had Firestone evac and recharge the system and I verified that all levels are fine. I can use a jumper wire and the clutch will engage when its hot and start blowing cold.

The aux fan runs almost continuously as well. It comes on around 110 degrees and never turns off regardless of what the a/c is doing. Not sure if this is relevant. Any help is appreciated.

92 4.0 Auto R134a

maybe a bad pressure switch

Update on my problems-
I took my Jeep to the A/C repair shop. The guy there checked out my A/C system to try and determine my problems. He had me turn on the a/c and then he stood and watched it to see if it would cycle. The A/c did not cycle in the 5 minutes that he was watching it, so he unplugged the low pressure switch and replugged it and as soon as he unplugged it the compressor disengaged. He then repeated the plug and unplug of the switch to make the compressor cycle several times. He then hooked up a vacuum machine with gauges to the high and low pressure sides to have a look at the pressures being produced by the system. The pressures checked out good. He then decided that maybe my a/c was a little undercharged so, he decided that he would pull vacuum on the system to measure the amount of refridgerant in the system. After the evacuation, it was determined that my Jeep had 1.25lbs of refridgerant in the system. But as it seems, for the most part the a/c now seems to be cycling. I am thinking about replacing the low pressure side switch anyway, because it doesn't cycle as often as I think it should. Will update after that is complete

dstef1605 said:

...,I am thinking about replacing the low pressure side switch anyway, because it doesn't cycle as often as I think it should. Will update after that is complete

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The compressor doesn't necessarily cycle on and off when the AC is on. It has to do with the cooling load on the system. With the fan on high, on a med/hot day, the compressor will run continuously, and that's normal. On a cooler day, or with the fan on the low setting, the compressor will cycle every 30 seconds to a minute or so.