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Unread 06-27-2009, 12:09 AM   #1
NighthawkMDX
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A/C Only Blows Hot Air, Plenty of Freon....

My 1999 Cherokee Sport has had an A/C issue over the past year and I have yet to find a solution for it. Last summer on hot days the A/C would work fine for about 10 minutes of driving and then would start blowing hot/humid air for 10 minutes before it would go back to being cold. This process would cycle constantly if you had the A/C on but luckily I made it to winter without suffering too bad. I tried putting freon in it thinking maybe it was low, but my gauge shows that it has plenty of freon. Now that summer is here this year the A/C has gone to only blowing hot air 100% of the time now. It still has plenty of freon but it will not blow cold air and driving the car has become a punishment. The compressor comes on just like it should, but like I said I only get miserable hot air. Does anyone have any ideas on what the problem might be?

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Unread 06-27-2009, 06:46 AM   #2
bjones71087
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Does the compressor cycle or stay on constantly? Any condensation? Do you have REAL guages or the "walmart" low side only guage?
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Unread 06-27-2009, 08:07 AM   #3
natertots
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Check your vacuum canister, if its not hooked up propoerly or has a crack/leak in it, your a/c wont work right. Mines in my bumper not exactly sure where yours is. Im sure someone will chime in with the location though. good luck.
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Unread 06-27-2009, 08:17 AM   #4
AZ Jeff
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Quote:
Originally Posted by NighthawkMDX View Post
My 1999 Cherokee Sport has had an A/C issue over the past year and I have yet to find a solution for it. Last summer on hot days the A/C would work fine for about 10 minutes of driving and then would start blowing hot/humid air for 10 minutes before it would go back to being cold. This process would cycle constantly if you had the A/C on but luckily I made it to winter without suffering too bad. I tried putting freon in it thinking maybe it was low, but my gauge shows that it has plenty of freon. Now that summer is here this year the A/C has gone to only blowing hot air 100% of the time now. It still has plenty of freon but it will not blow cold air and driving the car has become a punishment. The compressor comes on just like it should, but like I said I only get miserable hot air. Does anyone have any ideas on what the problem might be?
Let's start with the basics.
1. How do you know it has plenty of refrigerant? These modern systems are filled by WEIGHT of R134a, NOT pressure in the lines.
2. Assuming it has a confirmed proper charge of R134a, what are the high and low side pressures when running?
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Unread 06-27-2009, 08:38 AM   #5
NighthawkMDX
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Quote:
Originally Posted by bjones71087 View Post
Does the compressor cycle or stay on constantly? Any condensation? Do you have REAL guages or the "walmart" low side only guage?
The compressor cycles, and the lines/canister in front of the pass. side firewall have lots of condensation on them. I will have to check on the freon readings when I get back. I am currently out of town with a different car. I was hoping to get an idea of what to buy because I can get the parts at a discount where I am at for the weekend.
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Unread 06-27-2009, 09:13 AM   #6
bjones71087
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If the compressor is cycling on and off every few seconds, then it is starving for refrigerant, check the pressures with a good set of manifold guages. Best thing would be to go to a shop and have a vacuum held on it for at the very least 30-60 minutes. (to make sure there are no leaks.) and then fill it back by weight.
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Unread 06-27-2009, 09:21 AM   #7
dameono4
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My jeep does the same thing, seems like when the engine gets to operating temperature it stops working, but almost feels like the air is mixing with the heater. Removed the vacuum hose from where it enters into the firewall and is working. Would also like to know where the vacuum canister is located. Didnt mean to jack your thread but having the same problem.
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Unread 06-27-2009, 09:48 AM   #8
MJR
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First the system needs to be properly charged. All the R134a needs to be removed, and vacuum pulled on the system (removes moisture), and recharged to the proper level.

REFRIGERANT CHARGE CAPACITY
The R-134a refrigerant system charge capacity for this vehicle is 0.567 kilograms (1.25 pounds)

Too little or too much can cause problems. By your description it almost sounds like a bad low pressure cycling switch on the accumulator but could be other things.


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Unread 06-28-2009, 07:08 AM   #9
dmm219
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Quote:
Originally Posted by bjones71087 View Post
If the compressor is cycling on and off every few seconds, then it is starving for refrigerant, check the pressures with a good set of manifold guages. Best thing would be to go to a shop and have a vacuum held on it for at the very least 30-60 minutes. (to make sure there are no leaks.) and then fill it back by weight.
this is not necessariy true on an XJ (it is on a ZJ). The XJ's will cycle on and off to prevent your evap core from freezing up. This is normal on an XJ.
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Unread 06-28-2009, 07:12 AM   #10
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If the above suggestions don't identify the problem, check the compresson clutch. I had an issue last summer, with the exact same symptoms. Turns out the compressor clutch was slipping after about 10 minutes of use. After a while, it would catch again and work for a little bit before slipping again. If you search this forum, there used to be a writeup on how to clean and check the shims on the clutch to fix this. For me, this fix didn't work, and I had to install a whole new compressor.
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Unread 06-28-2009, 07:24 AM   #11
Goldenknob
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the vacuum canister is on the passenger side in the bumper, held on by 2 10mm bolts.
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Unread 06-28-2009, 12:59 PM   #12
rlitwin
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The a/c system seems to be working correctly, but you are still not getting cold air? You can clamp off the water hose going to the heater core to test your blend door. If your blend door isn't working, stopping the heat from getting to the heater core will get you cold air.
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Unread 06-28-2009, 01:04 PM   #13
bjones71087
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Quote:
this is not necessariy true on an XJ (it is on a ZJ). The XJ's will cycle on and off to prevent your evap core from freezing up. This is normal on an XJ.
it will do that on any car actually, what i was talking about is if it runs for a FEW seconds and comes back on for a FEW seconds. its the same on any compressor that is low on freon.
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Unread 06-28-2009, 01:16 PM   #14
MJR
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Quote:
Originally Posted by bjones71087 View Post
it will do that on any car actually
There are some vehicles that the compressor does not cycle and they use variable displacement compressors, just FYI but not Jeeps.
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Unread 06-28-2009, 02:14 PM   #15
compcrasher86
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I say check the A.C. clutch, because it could be slowly failing and now it just won't engage. Unplug the clutch connector w/ engine off and put 12v into it and see if it clicks (dont worry it may be loud) but if it doesnt click then your a.c. clutch is shot. Not extremely expensive but a minor inconvenience
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