A/C Question

So today, while driving the Jeep home from work, I decided that because it was so hot, that I would turn the a/c on so that I could cool the car down. Everything seemed to work as expected, except, I noticed when I stopped at a couple of traffic lights, the aux. fan seemed to be running the whole time that I was sitting still. This is not my first Cherokee with the 4.0L, so I know from past experience, that typically when you stop at a traffic light with the a/c on, that the aux. fan cycles on and off with the engaging of the compressor clutch. On my Jeep, it seems that the compressor clutch is not disengaging to cycle the compressor off. My drive home from work is not more than 5 miles and takes roughly 10 minutes in traffic, so I am not sure if the evaporator core is freezing up, but if I were to give it a good guess, I would almost be sure that it is, due to popping the hood when I got home, and looking at the refrigerant lines. The low pressure line was cold and the high pressure line was hot, but the low pressure line was so cold, that the condensate forming on them was beginning to freeze to the metal line. I have posted seveal times before trying to figure out what would be causing the compressor clutch to not reengage after the engine is hot and the system had been on, but now I am beginning to wonder if my problem may be faulty pressure switch. I have tried jumpering the switches to see if the compressor clutch would engage, but that did not make it kick on. I am thinking that maybe one of the pressure switches is sticking after the system comes on or is that even possible? Any help is greatly appreciated, before I have to take it to an a/c shop and pay out the butt to get it fixxed.

You need to determine if the engine is running too warm, it may not be related to the a/c.

Well I seem to have this issue to the "T". Everything works fine but when the engine is warm if I turn the A/C off and then back on the compressor will not engage. I can run a jumper wire to the compressor and it will engage and blow cold. I have been messing with the idea of just putting it on a manual switch. All levels are well within limits pressure wise and I have verified there are no leaks in the system. Engine never gets about 210. Im curious as to you guys thoughts on the OPs issue.

Model year?????????????????

I'm confused. Which problem are you having? The one were the compressor never disengages and you think it's freezing over, or the the one where, once it's hot and it disengages, it doesn't re-engage?

Just to clear the confusion up..It's a 1999 Cherokee Sport with the 4.0L.

Now as for the question of the problems that I am having, Saudade said:
"I'm confused. Which problem are you having? The one were the compressor never disengages and you think it's freezing over, or the the one where, once it's hot and it disengages, it doesn't re-engage?"

You are correct about my problems. The compressor never disengages and I think it might freeze over, but if I turn the system off once it's hot it will not re-engage again for some awhile, and then we can start the whole process over again!

dstef1605 said:

Just to clear the confusion up..It's a 1999 Cherokee Sport with the 4.0L.

Now as for the question of the problems that I am having, Saudade said:
"I'm confused. Which problem are you having? The one were the compressor never disengages and you think it's freezing over, or the the one where, once it's hot and it disengages, it doesn't re-engage?"

You are correct about my problems. The compressor never disengages and I think it might freeze over, but if I turn the system off once it's hot it will not re-engage again for some awhile, and then we can start the whole process over again!

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Ah, so you're having both. You have a high and low pressure cutoff switch that should cycle the clutch based on line pressures. I would suggest getting a set of manifold gauges and check the low and high side pressures. When you suspect the evap freezes over, do you feel reduced airflow out the vents? Is the air cool (not cold) or even a bit warm? Once you've waited long enough, how big is the water puddle underneath?

Not engaging once off when hot sounds like an air gap problem. There are shims behind the clutch that adjust the gap. After years of wear the gap increases and the electro magnets in the clutch can weaken to a point where they can't pull the clutch plate across the gap. If you tap on the clutch with a small hammer or screwdriver, engine running, ac on, you can typically get it to engage. If that happens, try adjusting the air gap. You can go to www.sanden.com for the service manual.

The air gap problem may not have consistant behavior. It may be intermittant, working sometimes and not other times. It is worth checking out. It took me 2 years to figure this problem out on my 2K GC! Now it works like a champ and with blend doors fixed..... wrong forum.