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A/C Crap Shoot

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Joined: 12 Aug 2007
Location: WNC

PostPosted: Sun Aug 12, 2007 11:28 am    Post subject: A/C Crap Shoot Reply with quote

I have a 99 Jeep Cherokee Classic with a 4.0 liter engine and 4-wheel drive. The Jeep has about 160,000 miles and I still love her more than my dog. But this summer the air conditioner has been acting up. It will usually start out blowing cold air from a fresh start (after sitting a while) but will start blowing warm air after about 15 minutes, and sometimes it will start blowing hot air after a while as well. If I am driving for 30 minutes or more, I can sometimes get it to blow cold or cool air again for a short period of time. But mostly, it seems that once all systems get up to normal operation temperatures, the air quits working.

I don't believe the a/c system is leaking due to the fact that it maintains a constant pressure from month to month. Could I be wrong about this? Would it maintain a constant pressure even if it were leaking?

My uneducated guess is that the compressor is bad, but I would like some experienced opinions before I fork out the big bucks for a new one. So, this is the information that I have gathered for you so far. 1. even when the a/c system starts blowing out hot air, the compressor clutch still turns. 2. if I remove the plug from the top of the canister, the clutch remains engaged. but if I leave the plug in, it engages and disengages properly.

And finally, I did add some booster coolant to the low pressure side and this did not help. However, it did boost the pressure up to the highest end of the safe range, which worries me. And as you might have guessed, the constant pressure measurements that I mentioned previously were taken at the low pressure valve with a basic gauge that I bought at Auto Zone. I have not taken pressure readings from the high pressure valve.

Can anyone guide me to what might be wrong or what I should check next?

Happy trails.....
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Joined: 23 Jan 2004
Location: I knew it...I'm surrounded by Assholes!

PostPosted: Sun Aug 12, 2007 12:45 pm    Post subject: Reply with quote

Just taking a measurement of low pressure is not going to give you an indication of how the system will perform (why places like Autozone even sell crappy gauges like that baffles me). You need to know both the low side and high side pressures, the ambient air temperature and the temperature coming from the vents to make any kind of real diagnosis.

Based on the symptoms, it sounds like the compressor is guess would be something like a bad condenser or evaporator coil.

97 XJ Sport with a bunch of stuff
Never argue with idiots, they drag you down to their level and beat you with experience
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Joined: 09 Aug 2007
Location: Stockholm, Sweden

PostPosted: Mon Aug 13, 2007 3:19 am    Post subject: Reply with quote

My 00 Cherokee Sport showed similar symptoms. I had an A/C expert check it and his conclusion was that the compressor clutch is not working properly. When the clutch gets hot it starts to slip. This would explain why your A/C is often working fine when you start (and engine, compressor etc is cold).


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Joined: 07 Sep 2006
Location: Visalia, CA

PostPosted: Thu Aug 16, 2007 11:34 am    Post subject: Reply with quote

I know that people think I'm probably crazy, and I've mentioned this before, but it is possible that your cpu is bad. My brother-in-law's 2000 XJ was having the exact same symptoms and the mechanic told us it was the CPU. Thinking he was crazy, we tested everything... relays, temperature sender, high pressure/low pressure sensor, clutch engagement, r-134 level. So we took it to another mechanic freind and he confirmed the diagnosis of CPU. He said when everything warmed up the CPU quit sending the proper signal to the relay to lock and unlock the clutch. To confirm the diagnosis, he by-passed the relay switch to force the clutch to be engaged. Sure enough, the unit blew perfectly cold air even when the engine was warm and working (except if you keep it this way for too long your whole system will freeze up... which is bad). So before you change out the clutch or pump, bypass the relay to know for certain whether your clutch is engaging properly or not. Of course, this may not be your problem at all, and then I've got nothing.
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Joined: 19 Jun 2007
Location: California

PostPosted: Thu Aug 16, 2007 12:25 pm    Post subject: Reply with quote

you have a few good answers here!!! IF you think you're going to take it to an ac shop----be very careful here!!! try and get some recommendations or something, these shops can really milk you dry quick and not fix the problem

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