Automotive Air Conditioning Information Forum (Archives)

Mudshack on Tue August 10, 2010 9:49 AM

Year: 1999
Make: Jeep
Model: XJ
Engine Size: 4.0L
Refrigerant Type: r134
Ambient Temp: 100
Pressure Low: 30-100

Well for months our A/C had worked for 20min then quit. Turn the A/C off and on every 1 min 4-19 times and it will start working again. Last night I pulled into the garage and it was working so I stuck the guage on the low side. It ran from 24-30psi while blowing cold (not very cold, but good). It stayed on......go figure. So I turned it off (back up to 100psi - ambient temp) then turned the A/C back on....the compressor kicks on, but the A/C doesn't blow cold...then it did it!!! I heard something like a switch click and the pressure dropped to 30psi and the cold air started.

What is making it not work?

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1999 Jeep XJ Sport

Mudshack on Thu August 12, 2010 9:27 AM

No one? Someone please give me an idea.

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1999 Jeep XJ Sport

fasto on Thu August 12, 2010 1:31 PM

I see you asked some questions in some other threads. I think an XJ is a Cherokee to us non-Jeepers? A few thing I learned from fixing a '99 Cherokee Classic:
1) You need to check if the compressor clutch is actually pulling in when the system is not cooling. The triangular plate on the front should be spinning. If it is not, the clutch is not pulling in. The cycling systems wear the clutch out, and you may need to adjust the clutch gap. Seach on "clutch gap" on this forum to find out how.
2) Cherokees use both an engine-driven fan through a fan clutch, and an auxiliary electric fan. Make sure the aux fan is running when the AC is on. Chrysler had complaints about the headlights dimming when this fan starts up so they added a "soft start" circuit to spin it up gradually. This fails almost invariably. Luckily it can just be unplugged and forgotten about. I don't remember where it is, trace the wires from the electric fan until you find it. Also, the engine driven fan clutch is worn out. Replace it.
3) You need to get a set of gauges and check the high side pressure when it's not working. Chances are that since the fan clutch is worn out and the electric fan is inop the system is cutting out on excessive high side pressures, unless it's got a leaky evaporator.
4) These cars, and all Chrysler cars of this vintage, are well known for leaky evaporators. The refrigerant leaks out slowly and the system becomes less and less effective. If the compressor is "short cycling" by clicking on for 5-10 seconds then off for 5-10 seconds the refrigerant charge is low, and almost certainly due to a leaky evaporator. Of course, this assumes that you've adjusted the clutch gap and fixed the cooling fans. You can sometimes check for a leaky evap by wiping the inside of the evaporator drain pipe with a clean white cloth. If it comes out greenish and slimy, the evaporator is a goner (assuming Chrysler put dye in the AC when the car was built).
Changing the evap in a 1999 Cherokee Classic:

Not too bad, book calls for 8 hours as I recall. This one took a little longer as I found the compressor's clutch was out of adjustment and the electric fan was inop.

Mudshack on Thu August 12, 2010 4:12 PM

Great write up. I didn't know about the elec fan. I will look into that. I will tell you that the compressor is spinning when I turn the A/C on from in the cab. And it is already spinning (blowing hot air) when I heard a click and the low side pressure dropped and cool air started blowing.

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1999 Jeep XJ Sport

fasto on Thu August 12, 2010 10:27 PM

While I don't want to start an argument something you said doesn't add up. This statement:
**
And it is already spinning (blowing hot air) when I heard a click and the low side pressure dropped
**
Are you absolutely sure? The symptom that you described is exactly cycling on high pressure, ie, the fans aren't up to snuff. Except, you say the compressor is turning! Something doesn't add up.
This generic picture of a compressor, from ackits.com, with arows added by your truly: (note it's not the same compressor as the Sanden on your Jeep)

shows the pulley on the outside with the red arrow, and the center "hub" with the silver flat springs attached to it with the green arrow. The pulley (red arrow) turns the entire time the engine is running. The hub only turns when the compressor is clutched in. Is the hub turning when warm air blows? The click you mention sounds like the clutch engaging. Please check again if the hub is turning when the low side is high and warm air is blowing.

The reason why I ask this again is that it's very unlikely that the fixed displacement compressor on your Jeep can have the hub turning and sometimes compress, and sometimes not compress.
Also, we need the high side reading when it's blowing warm.

98audiA4 on Fri August 13, 2010 7:48 AM

i had a 99 xj for a short amount of time with a clutch gap issue. +1 for that.

Mudshack on Fri August 13, 2010 9:31 AM

I just saw your post of with the picture of the compressor. Funny. As I was driving in 100+ heat to service last night, the A/C worked fine for the first 10 min of highway driving, and then the humid air started. I dropped my wife and kids off and went to find a parking spot. Popped the hood and wanted to check to see if the elec fan was working. Sure enough it was. And just because I was there, I looked at the compressor. It wasn't engaged. I looked back on the inside console to make sure I had it on A/C and not just fan (because I go back and forth between the two at about 30sec intervals and it sometimes kicks back on). It was on A/C......

So this time I had the A/C turned to on, and the compressor clutch was not engaged (compressor was not turning). If the system was just low on refrigerant, I would expect it to do short cycles on and off. But no work sporatically. I will add a little refrgerant today and see what happens.

Might be tearing it apart this Sunday to try and take a shim out if adding refrigerant doesn't work.

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1999 Jeep XJ Sport

fasto on Fri August 13, 2010 11:56 AM

DON'T add refrigerant just yet! Adjust the clutch gap first, that's probably all that you need to do. With the clutch off, a business card should just slide between the clutch and the pulley, and the clucth should not drag when disengaged.
To adjust the gap, you just have to unscrew the bolt in the center and pull the clutch driving face off, then remove one or more shims. Reinstall the clutch driving face and check again.
I made a tool out of 1/4" steel plate with three holes in the correct spots so that I could thread in three screws to keep the clutch face from rotating while I unscrewed the center bolt. The clutch face was tapped 1/4-20 as I recall.
I tapped a hole in the center to use the same tool as a puller to get the clutch face off.

Don't try to pry the clutch face off with screwdrivers or something like that, you'll destroy it. Also don't use a two-jaw or three-jaw gear puller. Use the three tapped holes.

PS, a quick and dirty check to see if there's enough refrigerant is to feel the suction pipe at the compressor while it's running and the outside temperature is hot, the hotter the better. If the suction pipe is nice and cold the refrigerant quantity is in the ballpark. Of course it's always best to recover the refrigerant and weigh in a new charge to be absolutely sure.

Mudshack on Fri August 13, 2010 1:04 PM

O'Reilly's rents the clutch plate puller for free. I will rent that on Sunday and tear into this.

I can't find any pictures online of this repair, nor any videos. Strange. Everyone wants to be a TV star now a days, but no one has made a video of this fix.

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1999 Jeep XJ Sport

fasto on Fri August 13, 2010 4:21 PM

The puller is for a Sanden compressor? I know they rent GM compressor clutch pullers, I didn't know about Sanden.

Adjusting the gap is pretty easy. Measure the gap using feeler gages or business cards so you've got an idea of how much to close it up. Turn the clutch plate by hand to get a feel for how it turns, later you'll compare this to make sure the clutch isn't dragging. Remove the center bolt and pull off the clutch plate. Don't lose the shim washers they're stacked up behind the clutch plate. Remove enough shim washers to get the clutch gap to about 0.020" or 1 business card thickness. Save the shim washers until you're done in case you need to make a few tries. Reinstall the clutch plate and center bolt. Check the gap to see if it's correct, also check that the clutch plate rotates freely by hand without dragging on the pulley (you can mentally compare to when you turned it before). Make sure everything is back together correctly and you're good to go.

I seem to remember that I had to take off the belt and unbolt the compressor to tilt it back far enough to get the clutch puller in there. I think it's almost inside the fan shroud. There was enough slack in the refrigerant lines that I didn't need to disconnect anything.

The Cherokee A/C drops the compressor clutch out when the evaporator is cold to prevent freezing (it actually cycles on low side pressure but the end result is the same). What happens as the clutch gap gets wider is the clutch can pull in when the engine bay is cold, but doesn't have enough magnetic force when it heats up to pull in again. Closing up the gap fixes this. Let us know it works out.

Rick-l on Fri August 13, 2010 5:10 PM

Can't you put a volt meter on the clutch to see if it is supposed to be running? Just to be sure it is not something electrical and there is no problem with the mechanicals.

ACProf on Fri August 13, 2010 9:44 PM

As intermittent as this problem seems to be - I'd hook an extra set of wires, one into the clutch coil wire (probly at the connector) and the other to ground. Then hook up an auto lamp (like a side lamp) to the other ends. Then whenever the clutch had power, the lamp would come on. A quick glance at the clutch would determine if its working right. Could also tap the clutch face with the wooden end of a hammer and see if it engages (when the light is on).

Mudshack on Fri August 13, 2010 10:30 PM

Good idea about the mallet. Unfortunately, it is located under the fan shroud, and only 1" from the spinning fan. I have yet to see it engage or disengage while the A/C unit is set to run.

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1999 Jeep XJ Sport

98audiA4 on Mon August 16, 2010 3:02 PM

if you have some sort of impact you can take the clutch nut off without the holder. when i did mine (99) after the nut was off the clutch came off very easily. i had 3 shims...removed 1 and the problem was solved.

JeremyB on Wed August 18, 2010 12:39 PM

Had excessive clutch gap problem with a 1999 and 2001 XJ. Similar symptoms as yours.

If I recall correctly:

Removed fan shroud bolts for mechanical fan and let shroud dangle for room.
Used square shaft screwdriver as a lever against 2 of the clutch fingers things to hold clutch as I removed clutch nut.

Fooled around and removed the clutch with a mallet, screwdriver, elbow grease. A/C shaft is splined.
Removed spacer(s) from compressor.
Installation reserve of removal!

The clutch face was well worn on the two I worked on. Wonder why these compressors are so susceptible to excessive gap growth.