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Need help with an AC problem


 
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Woodtroll
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Joined: 13 Jun 2008

PostPosted: Fri Jun 13, 2008 5:45 am    Post subject: Need help with an AC problem Reply with quote

Hello, folks!

I found this board while researching a Cherokee AC problem, so this is my first post.

I'm hoping someone here can help me with an AC problem on my wife's 2001 Cherokee. We bought this one last spring, after our 2000 was totaled in an accident. At that time, on normal AC, it would cool fine for a while, then eventually quit cooling, and began blowing warm air with the compressor cycling frequently. I took it to a local garage, who said it was a little low on refrigerant, and it worked okay the rest of the summer.

This spring, as the weather warmed, my wife said that it was again cooling for about ten minutes or so, and then warming up. Figuring that there was a leak, and wanting to learn something for myself, I decided to buy a set of gauges, some UV leak detector, and figure it out myself. (I am a tightwad, and it irks me to pay someone money to fix something, but I'll spend twice as much on tools and equipment to fix something myself, knowing I can face similar problems next time).

I hooked the gauges up, ran the engine and AC on Max Cool, and had the following readings (ambient air was 70 degrees F): Low 30, High 280, gradually increasing to Low 34 and High 300 just before the electric auxiliary fan kicked on, which brought the readings down to 25/200. The vent air was running 48-50 degrees. I ran it about 15 minutes in all, and it never did quit cooling; it seems to do this most in hot weather.

Now, I don't know much about newer AC systems, but this doesn't seem like a system low on refrigerant to me. I suspect the garage put more than necessary in, but how do you explain the fact that it worked normally last summer? I guess that either there is air/ moisture in the system, or the orifice is occluded, but the system appears to have the original Chrysler UV refrigerant in it, so I don't think it's ever been taken apart. Maybe it has been repaired, and this is not the original UV dye (?).

Can someone give me some pointers? If I pull a vacuum on the system, will I need to replace the pump lubricant? I assume the orifice is in the connection at the firewall, or do I need to replace the whole tube?

Any suggestions, thoughts, or pointers would be most appreciated. Many thanks!

Regan
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gopher383
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Joined: 20 Nov 2007
Location: V.A.

PostPosted: Fri Jun 13, 2008 3:16 pm    Post subject: Reply with quote

It sounds the same as mine in which case its the compressor isnt holding the coolent anymore maybe its cracked.
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Woodtroll
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Joined: 13 Jun 2008

PostPosted: Sat Jun 14, 2008 5:18 am    Post subject: Reply with quote

Thanks, Gopher. I think that it is holding the refrigerant in, as the voulme/ pressure seems adequate. I sure do appreciate your input, though.

I tried this again this morning. I also did some more digging yesterday, and found where someone listed the factory specs as being performed at 1500 rpm; my last readings had been at idle. I also flushed the condenser exterior well, even though it looked pretty clean. So the new test this morning:

Ambient 66 degrees, engine run to operating temp. then held at 1500 rpm by my able assistant (son), Low 20/ High 250, Condenser temps 154 inlet/ 128 outlet, 40 degrees at the vent, and the pressure after the system was shut down equalized within 20 seconds to Low 45/ High 49. It seemed to hold there, but that could be the gauges, perhaps?

Also, the condenser fan does not come on with the compressor; it seems linked only to high coolant temperature. Someone implied in another post that it should be linked directly with the AC compressor; is that correct?

As far as the dye, I assumed it was factory. There is a Mopar/ Chrysler sticker on the radiator support that states, "Note: This system has been treated with fluorescent leak detection dye. Use a UV style light to detect any leaks." This was new to me, too, but since it was an OEM sticker I figured it must be factory.

That may be the problem, then, that in the past the system was repaired and not properly evacuated?

Incidentally, I would have the garage up the road recover the Freon, and just let them have it. I have a vacuum pump here, designed for commercial AC, that should do the job. I assume that pulling the vacuum on this system would not affect the pump lubricant?

Does anyone have the factory manual, possibly, to make sure that I am following the correct procedure and have an accurate temp./ pressure chart?

Thanks very much for your help, folks!

Regan
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440_Magnum
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Joined: 18 May 2008
Location: Texas

PostPosted: Wed Jun 18, 2008 10:54 am    Post subject: Reply with quote

Woodtroll wrote:

Ambient 66 degrees, engine run to operating temp. then held at 1500 rpm by my able assistant (son), Low 20/ High 250, Condenser temps 154 inlet/ 128 outlet, 40 degrees at the vent, and the pressure after the system was shut down equalized within 20 seconds to Low 45/ High 49. It seemed to hold there, but that could be the gauges, perhaps?




Going from memory here, but 20 low side sounds a bit low for an R-134a system. In fact, I *think* the low pressure shutdown safety is supposed to trip at around 20 PSI to prevent a low system from inadvertently sucking in air and moisture, which it can do if the low-side pressure ever goes negative. My '99 came with an AC problem similar to yours, which turned out to be a leaking compressor shaft seal. It would kick on for a few seconds, and whenever the low side pressure hit ~20 psi, the safety would kick it off again.

Quote:

Also, the condenser fan does not come on with the compressor; it seems linked only to high coolant temperature. Someone implied in another post that it should be linked directly with the AC compressor; is that correct?



Quote:

Does anyone have the factory manual, possibly, to make sure that I am following the correct procedure and have an accurate temp./ pressure chart?

Thanks very much for your help, folks!

Regan


Got an FSM, but its at home. I'll try to remember to dredge it up tonight and post the relevant info. Its got a graph of condensor outlet temp vs. high-side pressure which indicates whether the charge is correct, so you've gathered all the pertinent info, I'll just have to look up 128 degrees/250 PSI and see if that's in the happy zone or not. Going from memory (yeah, yeah, shaddup already Wink ) I think its just a tick low on refrigerant.

Just as an "oh by the way," the '99 Cherokee (and I assume your 01 also) uses a low-side accumulator/dryer (GM-style) instead of the more typical Ford/Mopar high-side receiver/dryer. What that means is that it gets by with a much smaller refrigerant charge- 1.25 pounds for my Cherokee vs nearly 4 pounds for my wife's Vision TSi- since the low-side accumulator holds much less liquid refrig. than a high-side receiver/dryer. The downside is that a small leak will start to affect a low-side accumulator system WAY quicker than a high-side receiver system since there's less reserve available. A leak that might need a charge less than once a year on my wife's car will need a charge every few months on the Cherokee, so the system really needs to be tight.
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Woodtroll
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Joined: 13 Jun 2008

PostPosted: Wed Jun 18, 2008 3:57 pm    Post subject: Reply with quote

440 Magnum,

It now looks like the compressor clutch may be the issue; when the warm air starts, the clutch is getting power but not engaging. I may have to "touch up" the charge a little, but please hold off on doing any heavy duty digging until I have a chance to tinker some more; maybe I can adjust the air gap and get this thing going again. Unseasonably cool weather here the past few days has delayed my diagnosis attempts!

Thanks very much for your help, I sincerely appreciate it!

Take care, Regan
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440_Magnum
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Joined: 18 May 2008
Location: Texas

PostPosted: Wed Jun 18, 2008 4:08 pm    Post subject: Reply with quote

Woodtroll wrote:
440 Magnum,

It now looks like the compressor clutch may be the issue; when the warm air starts, the clutch is getting power but not engaging. I may have to "touch up" the charge a little, but please hold off on doing any heavy duty digging until I have a chance to tinker some more; maybe I can adjust the air gap and get this thing going again. Unseasonably cool weather here the past few days has delayed my diagnosis attempts!

Thanks very much for your help, I sincerely appreciate it!

Take care, Regan

The clutch air-gap could be the problem- when the coil gets hotter the magnetic field gets weaker, so too much air gap can definitely keep it from kicking in! IIRC, the Sanden 7 series uses shims to set the air gap and it can be done without removing the belt.

As for the rest- there was nothing "heavy duty" about the digging, the FSMs for the '66 and 69 Dodges and the 93 and 99 Eagle and Jeep are all on a shelf in the garage. The Jeep FSM didn't actually have a pressure/temp chart like I thought I remembered. It just says "evacuate the system and put in 1.25 pounds" to get the right charge. Yeah. Real helpful-if you want to justify the cost of a refrigerant recovery machine... pissed Anyway, I pulled out the '93 Eagle Vision FSM which does have an R-134a temp/pressure chart, and my memory was close. To be in the middle of the happy zone at 128 degrees condenser outlet temp, you should have a high-side pressure of around 275-280. But 250 is on the low edge of the happy zone, so its not too far off and probably isn't the whole problem. It might still need a small shot of R-134 when everything else is squared away.

Good luck, and let me know if I can help. I'm new here too, so its nice to be on the helping end for a change. Oh, and send some of that cool weather this way- 101 AGAIN today in Austin. And not even July yet! Shocked
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DavidXJ
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Joined: 07 Sep 2006
Location: Visalia, CA

PostPosted: Mon Jun 23, 2008 7:31 am    Post subject: Reply with quote

Quote:
Also, the condenser fan does not come on with the compressor; it seems linked only to high coolant temperature. Someone implied in another post that it should be linked directly with the AC compressor; is that correct?


I don't know much about all the technical stuff you guys are talking about, but I know that the auxilary fan should absolutely turn on and off with the A/C pump, and if it doesn't, the system will not cool properly.
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Brad The Best
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Joined: 14 Jan 2007
Location: Kamloops B.C Canada

PostPosted: Sat Jul 19, 2008 3:16 am    Post subject: Reply with quote

you got a sight glass on the canister ? see any bubbles ?

fan comes on when ac comes on no excuse . David is right .

i would get it evacuated and re charged . don't know what thats worth since i do my own .
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