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A/C Stops Working, High Pressure In Low Side.

db209_2000

NAXJA Forum User
Location
Albany, NY
My '98s air conditioning stops working while I'm driving. It starts blowing warmer air out the vents. I've pulled over just after it stops to check everything and found that I have high pressure in the low side of the system, and the Efan runs constantly. I don't think it's evaporator freeze-up because the volume of air doesn't change. Could it be a clogged orifice tube?

I'm familiar with expansion valve systems because they have problems all the time, but I've never had to diagnose an orifice tube system. The system is fully charged. With all the t-storms in Upstate NY lately, it's hard to drive looking through a fogged windshield.
 
How High is high? Do you have a high pressure reading?

Is the compressor engaged when you check?

Could be fan clutch needs to he reshimmed.
 
No, I don't have a pressure reading, and the clutch gap is ok. I tried checking the pressures at work on a day off, but as long as I'm not actually driving it'll work just fine. I let it sit for at least 20 minutes with the gauges on and all was well, 10 minutes into my drive home it stopped again. The low side line is just as hot as the high side (going by feel only), the electric fan constantly runs, but the compressor won't engage. If I shut of the engine for about an hour I can get it to work again for about another 10 minutes.
 
That can happen if you overfill the system. There is a high side, excessive pressure, safety switch.
 
It is difficult to diagnose many A/C problems without a set of manifold gauges.

It is not clear to me how you can say the clutch does not need to be reshimmed if the compressor is not engaging.

For this to be true, you would have needed to determine that electrically the system is not telling the clutch to engage the compressor. That would mean either the low or high pressure switches are failing or that the high pressure side is so high that it is disengaging the clutch.

Have you done this?

Usually the clutch reshimming cures intermittent A/C compressor engagement problems, particularly after the system has been running for a while.

You could remove the high pressure switch and jump the contacts to see if the compressor clutch will engage. If you do this, the only other overpressure safety in the system is the compressor overpressure mechanical valve.
 
It is difficult to diagnose many A/C problems without a set of manifold gauges.

It is not clear to me how you can say the clutch does not need to be reshimmed if the compressor is not engaging.

For this to be true, you would have needed to determine that electrically the system is not telling the clutch to engage the compressor. That would mean either the low or high pressure switches are failing or that the high pressure side is so high that it is disengaging the clutch.

Have you done this?

Usually the clutch reshimming cures intermittent A/C compressor engagement problems, particularly after the system has been running for a while.

You could remove the high pressure switch and jump the contacts to see if the compressor clutch will engage. If you do this, the only other overpressure safety in the system is the compressor overpressure mechanical valve.

Electrically it is not being commanded on after driving. I don't have my own set of manifold gauges, but the a/c evac and recharge station at the shop I work at does. The system is filled with 1.25 lbs of R-134A per the sticker. Sitting in my bay at work everything is fine with the air conditioning system, all the pressures are normal. The compressor shuts off completely while I'm driving, the low side line feels hot to the touch, the electric fan continues to run, and I get very warm air out the vents with no change in volume of air.

Is this a better explanation? Could this be a clogged orifice tube?
 
My next step would probably be to replace or test and then replace the pressure switches.

You can jumper them one at a time and see what happens.

With the fan running all the time, I'd start with the high pressure switch. Its a binary switch and controls both the e-fan and disengagement of the clutch (at least on the later Cherokees).
 
If your compressor is not running, both hi and low side lines will get hot from engine heat radiating its energy around the engine compartment. My guess, is the electromagnet in the clutch is weak. It also makes sense that the e fan is constantly running, because it's trying to turn on the compressor clutch but it never does. Also, when the compressor is not running the refrigerant will stabilize between the Hi and Low side. That's why the low side has higher pressure than normal. When AC is on, and it's not working, check for voltage at the compressor. And like someone else said, you need some gauges.
 
Finally, a day without rain! Got a chance to really get into it. IH392 you were right, the low side feels hot due to underhood temps. It's not the pressure switches either. I drove home with everything off. Got home, popped the hood and turned on the A/C. The electric fan turned on, but the compressor did not engage. I checked the positive wire with a light and found it was getting power. The ground was good. Open circuit through the clutch coil after heating up :( That would explain why it never acted up while I had the hood open checking the pressures.

So now I gotta replace the coil, or get a new compressor, whichever is cheaper. Thanks for the help all!
 
.........
So now I gotta replace the coil, or get a new compressor, whichever is cheaper. Thanks for the help all!

Your compressor is 16 years old, if it's stock. The compressor clutch could be the next thing to go. I would say cut your losses and just get a new compressor at this point.....
 
Does your AC start blowing hot air when you are at low speed or high speed or doesn't matter.

if your AC stops working when you are in the city then starts working when you get on the freeway it could be as simple as your cooling fan.
 
Does your AC start blowing hot air when you are at low speed or high speed or doesn't matter.

if your AC stops working when you are in the city then starts working when you get on the freeway it could be as simple as your cooling fan.
Your compressor is 16 years old, if it's stock. The compressor clutch could be the next thing to go. I would say cut your losses and just get a new compressor at this point.....

Doesn't matter how fast I'm going. 4 month old electric fan, 6 month old mech fan clutch. It's definitely the compressor. Thanks Oban. Ivan, since I can't find a clutch & coil to rebuild with, and RockAuto having a new compressor for only $150, I think I'll replace the 14 year old compressor (the original seized while under warranty at only 2 years old).
 
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