99 Cherokee AC Cycling Problem

[gkettman]

My AC was getting weak. Seemed normal enough after 5 years. I had a standard service performed. It was down a bit on freon (or whatever it's called these days) but nothing alarming. They evacuated and charged the system. It worked great... for about 5 minutes. We took a look and found that the fan clutch was not working. The cooling fan was spinning freely. The shop fixed that and I was out of time and had to go. The problem still exists.

Basically, the AC works great for about 5-10 minutes. Then it just stops working for at least 10 minutes or so. Then it will work for a few cycles, say 2-3 minutes, and then quit for say 5 minutes and then work. Finally, after an hour or two it works almost OK although it's a bit erratic, blowing quite cool for a bit and then quitting for 30 seconds to a minute. This pattern seems to apply whether I'm driving (on the highway) or stopped in traffic. It seems better when ambient temperature is lower. So, if it's in the low 70's it seems to work better than if it's 90 degrees. That doesn't make sense to me since you'd think the highway / stopped in traffic would have far more impact.

First, any suggestions? Second, what exactly are we discussing here in the way of circuitry. I know there's a high pressure cutout and a low pressure cutout. The low pressure seems unlikely. There doesn't seem to be any kind of cutout for "high acceleration" or "full throttle". Is there any kind of heat or temperature sensor on the compressor? I'll try to find a manual that covers this stuff but experience tells me that a good wiring diagram is hard to find (Unless you want to go to the dealer and spend a couple of hundred dollars). Does the computer have any input or control?

Thanks for any help. I don't work on cars much anymore. I do have a mechanic I like but I've had far too many bad mechanics in the past to not want to understand what's going on myself.

[Dale Aeppli]

Originally Posted by gkettman

My AC was getting weak. Seemed normal enough after 5 years. I had a standard service performed. It was down a bit on freon (or whatever it's called these days) but nothing alarming. They evacuated and charged the system. It worked great... for about 5 minutes. We took a look and found that the fan clutch was not working. The cooling fan was spinning freely. The shop fixed that and I was out of time and had to go. The problem still exists.

Basically, the AC works great for about 5-10 minutes. Then it just stops working for at least 10 minutes or so. Then it will work for a few cycles, say 2-3 minutes, and then quit for say 5 minutes and then work. Finally, after an hour or two it works almost OK although it's a bit erratic, blowing quite cool for a bit and then quitting for 30 seconds to a minute. This pattern seems to apply whether I'm driving (on the highway) or stopped in traffic. It seems better when ambient temperature is lower. So, if it's in the low 70's it seems to work better than if it's 90 degrees. That doesn't make sense to me since you'd think the highway / stopped in traffic would have far more impact.

First, any suggestions? Second, what exactly are we discussing here in the way of circuitry. I know there's a high pressure cutout and a low pressure cutout. The low pressure seems unlikely. There doesn't seem to be any kind of cutout for "high acceleration" or "full throttle". Is there any kind of heat or temperature sensor on the compressor? I'll try to find a manual that covers this stuff but experience tells me that a good wiring diagram is hard to find (Unless you want to go to the dealer and spend a couple of hundred dollars). Does the computer have any input or control?

Thanks for any help. I don't work on cars much anymore. I do have a mechanic I like but I've had far too many bad mechanics in the past to not want to understand what's going on myself.

HI, LOOK UNDER THE HOOD RIGHT BEHIND THE BATTERY THERE IS A POWER DISTRIBUTION BOX IT CONTAINS RELAY FOR A/C THE RELAY MAYBE TRIPPING IT OFF. IF YOU WANT A MANUAL WITH WIRING DIAGRAMS GET A CHILTON MANUAL # (8143) 84-98 $ 23 WORTH EVERY PENNY DALE [email protected]

[chris moore]

I have a pair of Cherokees, and the 2000 model I own began giving me the same symptoms that you have described. The bad news is that it only will get worse.
Through some basic detective work, I found that when the A/C was not cycling, the compressor clutch was still getting voltage, and, was well grounded. This led me to believe that the clutch coil was failing at certain high temperatures. Once it cooled off for a few minutes, the clutch would engage, and the A/C would work for a while, until the coil overheated again. I hope this helps you solve your gremlin ,But good luck finding reasonably priced parts.( try sanden.com, very helpful!)

[gkettman]

Chris: Thank you very much for the response. As you suggested it's done nothing but gotten worse. I had slowly worked backwards isolating the problem. It's not always easy since it takes 5-10 minutes to fail, etc. At any rate, I'd reached a point where I put an LED on the line just before the clutch and run it into the dash. Clearly there is voltage. I've eliminated a faulty ground and I replaced the little diode. That only left the clutch but it seemed very weird that a clutch would fail, but only when hot. So, you're seconding that idea reassures me that this is indeed the issue. Like you said, it seems impossible to get a clutch. Well, it's possible to get a clutch but it's $250 or so and you can buy a whole new (rebuilt) compressor, with clutch for the same price. I was also told to replace the receiver/dryer at the same time.

Thanks again, it really was very helpful information. Take care

[cas297]

I'm getting this exact same issue on my 1999 Jeep Cherokee Limited. It has gotten to the point were it very rarely will start the a/c or any fans. Did you guys find a solution? I'm about to take it to the shop but I want to give them somewhere to start to save me some $ on labor. Is this something that a beginner can do themselves or do you recommend to leave it to a prof.