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Grand Cherokee A/C Weirdness

ckzj on Thu June 12, 2014 2:08 PM User is offline

Year: 1994
Make: Jeep
Model: Grand Cherokee (ZJ)
Engine Size: 4.0
Refrigerant Type: R-134a
Ambient Temp: 70
Pressure Low: 52
Pressure High: 320
Country of Origin: United States

Hi everyone I'm hoping someone can help.

I have a 1994 Jeep Grand Cherokee with Air Conditioning, I've owned the vehicle for the better part of a decade. The A/C has always performed satisfactorily as long as I was moving and not stuck in traffic. If I stopped at a traffic light for too long the engine temp would climb and within a minute or two the A/C would kick off until I got moving again and cooled the vehicle down. I didn't think this was a big deal since nearly every jeep I've ever owned acted the same way and when you were moving it did a very good job cooling.

However as time went on the A/C became a little more tempermental. Initially I chocked this up to needing a seasonal charge, as I would put a can of 134a in and the A/C performance would come back and last most if not all of the summer season. (relatively short hot season in New England) Either way as time went on these charges I did would last less in duration and I found myself charging the system twice a summer, then I had to do it before I ever went on an extended trip.

A few years back I had to replace the engine, the condenser was removed and we put in the new engine.(this is the only time my A/C system has been open to the atmosphere since I have owned the vehicle) We used that opportunity to have my good friend at a professional auto mechanic shop to evacuate, vacuum test and charge the A/C, (that was about 5 years ago) The A/C worked ok but still pretty tempermental. Shortly after the new engine the vehicle was parked for 2 years for major suspension work and a few other things. Now that the vehicle is back on the road I want to get the A/C worked out as I am moving south and no A/C is not an option.

Be that as it may 2 weekends ago I put a can of 134a in and hoped for the best, I got A/C for about 30 seconds, decent temps and then the a/c compressor kicked off and was effectively not cooling for me so I went and saw my friend in the shop. We evacuated the system again, he said there might have been some residual air in the system and this should get any remaining air out and we hoped for the best. Long story short on the way home I thought we were in great shape but 2 minutes down the road I lost A/C again.

I went and bought a set of 143a manifold gauges to try and help me diagnose what's going on without bothering my friend at his shop.

When I hooked the system up and opened the valves my pre run pressures were 110 and 110 low and high respectively. When I turned the A/C on for a performance test using the procedure listed in the Jeep FSM for my vehicle the A/C kicked on, I got close to 48 degree air for a minute or two and then it shut off. Shortly before the A/C shut off my pressures were roughly 52 and 320, then the compressor kicked off. It tried once or twice immediately after kicking off to reengage but it didn't stay engaged for more than a fraction of a second. Shortly after that the pressures returned to their pre test values and the A/C didn't try and do much unless I went in the cab and cycled the switch for A/C, then the compressor would sometimes immediately kick on but not stay on longer than 2 or 3 seconds.

Not sure what to do next but for the record I have a friend with professional equipment if someones instructions merit that kind of attention so no worries there.

Any ideas..? I swapped the A/C relay with the starter relay on my power distribution block under the hood (same exact relay) but no change in behavior and the vehicle starts normally too so I think the switching relay is not the culprit.

The test procedure in the FSM stated get vehicle to full operating temp and in at least 70 degrees ambient temp bring RPM's to 1100-1300 put A/C on recirc, full blower, upper vent with a/c switch on and all windows and doors open and if the compressor cycles disconnect the plug on the accumulator and jump the 2 wires for test duration (I did this). The vent temp got down to 50 but the FSM says it should be closer to high 30's for that ambient temp.

When the compressor is working, one line on the compressor is hot as hell, one cold as antarctica. The accumulator, both lines pretty damn cold. The line running into the cab to the evaporator is pretty cold (the one with the low side fill/svc port).

Not sure where to go with this next except to defer to the experts here. When the A/C did work as long as I can remember when I shut off the vehicle there was a very loud hissing noise that initially I thought was a leak but it's just a hissing sound inside the plumbing that goes away within a minute of being shut down as pressures equalize.

Any thoughts?

Edited: Fri June 13, 2014 at 12:17 AM by ckzj

mk378 on Thu June 12, 2014 2:24 PM User is offline

It should stay running at those pressures. The pressure switch on the accumulator could be bad. Or the clutch gap is too wide, so it does one cycle then doesn't re-engage. Check that the clutch coil is getting power when it is supposed to be on.

It appwers that you also still have a refrigerant leak (very likely one or more of the springlock connections), and a bad fan clutch is what causes the condenser and engine to overheat when the Jeep is sitting still. 320 high side in 70 degree ambient means there's a problem with getting heat out of the condenser, this is why the vent temp was not that good.

Edited: Thu June 12, 2014 at 2:30 PM by mk378

ckzj on Thu June 12, 2014 2:32 PM User is offline

Wow the Internet connection at work is causing me grief...

Edited: Thu June 12, 2014 at 2:37 PM by ckzj

ckzj on Thu June 12, 2014 2:36 PM User is offline

I can post a video of what the compressor does later on tonight, and I can also check for voltage at the clutch.

It's also worth pointing out that The first time I fire up the A/C it works for close to 1 minute maybe 2 but after that, it's acting as I described. It acts this way even when I am driving as well. This vehicle has a single fan with a fan clutch, I can replace it but I know it engages when the engine is hot, just maybe not soon enough.

Also I was bypassing the pressue switch for the test per the FSM instructions...

Edited: Thu June 12, 2014 at 2:39 PM by ckzj

webbch on Thu June 12, 2014 3:49 PM User is offlineView users profile

What mk378 said. My vote is on the clutch gap for the cycling problem. Fan clutches are very deceptive. Spin it in your hand and it doesn't free-wheel, so you think it's OK. But on the vehicle, it just doesn't do the job. Install a new one, and you notice a big difference in engine temps at idle.

Pretty quick leak to drop a full can of 134a in 30 seconds. That's good - it should be easy to find.

ckzj on Thu June 12, 2014 4:47 PM User is offline

Ok thank's for the responses guys. I haven't fully reviewed the chapter on A/C in the FSM yet, is it safe to assume this will be a feeler gauge test and that there will be specs in there somewhere..?

ckzj on Thu June 12, 2014 4:48 PM User is offline

Also my friend and I added a shot of dye but it's not been running long enough I think, but maybe, who knows.

webbch on Thu June 12, 2014 9:52 PM User is offlineView users profile

The FSM will likely have a reasonable system description of the ac, but not a great "intro to auto ac systems" if that's what you're looking for. It will, however, tell you refrigerant capacity (and refrig oil capacities), which you'll need to know. Reading a bunch of posts here and picking up this book from the site sponsor are what helped me get started.

Edited: Thu June 12, 2014 at 9:53 PM by webbch

ckzj on Fri June 13, 2014 12:01 AM User is offline

I will look into the book but not necessarily looking to become an expert on the subject matter, although I bet it's full of good info and I still might grab it if you think it can be used as a manual / how to troubleshoot guide rather than a text book.

What I can say is I have a solid macro level understanding of the basic concepts on this particular system, the principals at work, components involved. I'm mechanically competent and have professional mechanical help at my disposal but none of us are experts on A/C system troubleshooting when it gets this weird.

What I am betting is going on is a bit of jeep weirdness and possibly some a/c system issue

When I went to record the video to show what the clutch was doing, the system ran like a champ. The ambient air temp was 68 not the technically the required 70 and I forgot to get a high idle going and the clutch switch on the accumulator was not jumped just plugged in but it ran until I shut the truck off 5 mins later (I was getting low on gas). The coldest the air got was 48 inside. I thought I might be in good shape for at least the ride home so I went inside and left the vehicle to sit a few hours. On my ride home it had cooled to 65 out and the and the A/C did not even attempt to engage. When I got home I shut the truck off restarted it and for giggles hit the a/c button, the compressor turned on, pressures were not that far deviated from the previously posted numbers when I hooked up the gauges.

For the record I've never had it work that well when it was warm out the last few weeks but the total non-cooperation of the system on the way home is perplexing. If pressures are ok, the a/c request light turns on when I hit the switch (I know that doesn't mean the signal is necessarily getting where it needs to go, just that the light on the a/c switch still works), not even on defrost did the compressor turn.

I can't check the gap on the clutch because the pulley's edge is flared beyond the gap so there's no clear shot but it ran like a normal a/c and the compressor didn't disengage even when I gradually increased the engine speed up to over 3200.

Also if the engine is not completely up to temp will that interrupt the compressor signal until it is warmed up..? I could have sworn I've seen it run in the middle of winter when defogging the windshield. Shortly after engine startup on some darned cold days!

I will get a fan clutch, and test the circuitry for the compressor clutch as the FSM indicates, voltage, amperage, etc but do you think it makes sense to have my friend evacuate the system and see how much refrigerant came out compared to what he put in last week? I didn't visually see any leaking at the snap spring connections but we will use the light and glasses tomorrow. He has a huge spotlight for it.

ckzj on Fri June 13, 2014 1:54 AM User is offline

I have later found that there is a section on the compressor clutch and air gap specs, so if I take it apart I will check it. (doesn't look bad to do but doesn't look fun either)

Right now your right I need to make sure the coil's getting the signal when it ought to. I'll test the HP and LP switches and the coil lead.

webbch on Fri June 13, 2014 1:55 AM User is offlineView users profile

Re clutch gap - I'm assuming you were trying to measure the gap. Another way to do it is to start the engine and turn on the a/c. If the compressor is not engaging when it should be, give the clutch a slight tap with a small hammer (if you can do so safely). If that causes it to immediately engage, you've found your problem.

Of course, I'm not familiar with your engine compartment to tell if that's any easier...

ckzj on Fri June 13, 2014 11:30 AM User is offline

Yeah I can tap it with a mallet safely, darned good idea I'll try that too!

ckzj on Tue June 17, 2014 11:54 PM User is offline

Ok, clutch is fine, tested it vigorously with a power probe and it didn't miss a beat. Doesn't appear to be much of a leak (yet) we pulled out a few ounces less than we put in but we just swapped hoses on the A/C unit. I'll test that later on in the season.

Also when we cooled the condenser with a hose the compressor kicked off at 36psi low side consistently. I replaced both high and low switches and o-rings, now I've just gotta get heat out of the loop like you guys said, I'm always tripping the hpco.

For now I've ordered replacement liquid line, severe climate orifice tube, accumulator, condenser (Mine's pretty hammered), severe duty fan clutch.

I couldn't find any leaks in the engine compartment at anywhere let alone at the spring lock couplings.

Hopefully this makes the system happy!

mk378 on Wed June 18, 2014 12:04 AM User is offline

Don't use the variable OT, it's just a gimmick. Stay with a stock one.

ckzj on Wed June 18, 2014 11:08 AM User is offline

Huh, I didn't realize it was an "Automatic Adjusting" device. It appears all the severe climate units are this way.

Sounds like a great way to introduce another point of failure into the system. Now I have to find out about my vendors return policy!

4.0_olds on Fri June 20, 2014 9:40 PM User is offline

I didn't read through the whole thread so sorry if this has been covered. I have a '93 Grand Cherokee and about every 2 years I needed to charge the system. It turned out to be the o-rings on the compressor ports. I believe they were black and I replaced them with green ones. This was done in 2006 and I haven't had to touch the system since.

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