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4wheel98cherokee
September 5th, 2010, 16:02
Hi guys, as the title says, I have a 1998, with the 6 in it, and I have a problem with the A/C. I have not touched the A/C or replaced anything on it since I bought my Jeep. It has always worked perfectly.

Today I started up my Jeep, turned the air on and drove it for about 10 mins with no problems. Suddenly, I noticed the air wasn't blowing cold anymore. In addition to the air warming, I could smell a odor in relation to the air shutting off (Note: It was not a burning smell, just a weird smell when you shut off the air conditioning but keep the fan blowing). Well after about 10 seconds or so of driving, the air came back on ice cold again. It did this about 3 times or so during a 20-25 min drive.

Could this be a symptom of a faulty cycling switch? Or perhaps the system is losing freon? If so why would it work perfect, shut off, then return? Any input would be greatly appreciated. It's way too hot to not have good working air! Thanks guys!

CharlesS
September 5th, 2010, 16:22
There is a sensor screwed into the accumulator/drier near the firewall on the passenger side that disengages the clutch to stop the evaporator from getting iced up.
The cycling is a safety feature for the compressor and is more than likely due to a low charge of R-134a.
Look carefully at the fittings on the lines going to and from the compressor, the condensor coil (in front of the radiator) and the compressor shaft. See if you notice any dampness that is caused by oil seaping thru the seal(s).
You should have the system pressure/temperature checked to verify how low on refrigerant your system is.

heyhar
September 5th, 2010, 16:22
It may be low on R134 (technically not 'freon'), or possibly it's freezing up. Maybe try to find the source of the smell, as a clogged chamber around the evaporator may be causing the malfunction. The evap needs a flow of warm air to keep it from freezing, and if the area is loaded up with rotting or moldy material, it may be impeding airflow, causing icing, (and the musty smell) and the shutdown of the compressor. Typically, a system low on refrigerant will blow, just not as cold, until there's too little in the system to close the switch. If you're getting a good, cold blast, that just stops, and later comes back, start looking for an airflow problem first. Rule out all of the easy, cheap, or free stuff first, before throwing money at a professional. You may be surprised at what you'll find under the cowl vent cover.

Ivan
September 5th, 2010, 17:03
There is a sensor screwed into the accumulator/drier near the firewall on the passenger side that disengages the clutch to stop the evaporator from getting iced up.
The cycling is a safety feature for the compressor and is more than likely due to a low charge of R-134a.
Look carefully at the fittings on the lines going to and from the compressor, the condensor coil (in front of the radiator) and the compressor shaft. See if you notice any dampness that is caused by oil seaping thru the seal(s).
You should have the system pressure/temperature checked to verify how low on refrigerant your system is.

This ^^^

It's most likely the low pressure switch on top of the accumulator. It's a simple swap out. Just get a new one at the dealership. You won't lose any refrigerant when you replace it, as there's a schraeder valve there to keep refrigerant in. As mentioned, your evaporator is icing up and blocking air flow, which is why you are getting the warmish air. Once the ice melts (about 20 minutes or so) the AC works fine until it ices up again, and the cycle repeats.

A tale-tell sign is large amounts of water under your rig once its sat for a while. That's all the ice melting off.

Low refrigerant could be another issue as well.

4wheel98cherokee
September 5th, 2010, 17:13
There is a sensor screwed into the accumulator/drier near the firewall on the passenger side that disengages the clutch to stop the evaporator from getting iced up.
The cycling is a safety feature for the compressor and is more than likely due to a low charge of R-134a.
Look carefully at the fittings on the lines going to and from the compressor, the condensor coil (in front of the radiator) and the compressor shaft. See if you notice any dampness that is caused by oil seaping thru the seal(s).
You should have the system pressure/temperature checked to verify how low on refrigerant your system is.

So a system that is low on refrigerant would blow cold, fade out, and blow cold again? And if it is low, that means it's leaking out right? If it all leaked out, it shouldn't return back to cold, no? I will check the accumulator to see if it froze up, my question is what would cause it to freeze? How do you prevent it from happening?

4wheel98cherokee
September 5th, 2010, 17:16
A tale-tell sign is large amounts of water under your rig once its sat for a while. That's all the ice melting off.



I did have a large puddle of water dripping from the bottom of my rig, I thought it was a unusual amount. I'm gonna try picking up a switch and see if that works. Thanks for the input.

4wheel98cherokee
September 5th, 2010, 17:19
It may be low on R134 (technically not 'freon'), or possibly it's freezing up. Maybe try to find the source of the smell, as a clogged chamber around the evaporator may be causing the malfunction. The evap needs a flow of warm air to keep it from freezing, and if the area is loaded up with rotting or moldy material, it may be impeding airflow, causing icing, (and the musty smell) and the shutdown of the compressor. Typically, a system low on refrigerant will blow, just not as cold, until there's too little in the system to close the switch. If you're getting a good, cold blast, that just stops, and later comes back, start looking for an airflow problem first. Rule out all of the easy, cheap, or free stuff first, before throwing money at a professional. You may be surprised at what you'll find under the cowl vent cover.

I will look into this and see what I find out. Thanks for your input, I will let you know what happens.

CharlesS
September 5th, 2010, 17:40
So a system that is low on refrigerant would blow cold, fade out, and blow cold again? And if it is low, that means it's leaking out right? If it all leaked out, it shouldn't return back to cold, no? I will check the accumulator to see if it froze up, my question is what would cause it to freeze? How do you prevent it from happening?


Since the entire system only holds about 1lb 4oz of R134a; then it wouldn't take much for the system to be low.
If the system is a few ounces low then the compressor will run until the setpoint of the sensor (screwed into the accumulator) is activated (low refrigerant pressure/temperature) to stop evaporator from totally freezing up at which time the clutch will disengage. Once the system pressure/temperature climbs above the setpoint the clutch will reengage and the air will get cold again.
The solution would be to have the system operating pressure checked for proper charge.

4wheel98cherokee
September 5th, 2010, 17:58
The solution would be to have the system operating pressure checked for proper charge.

Okay, I will have the system pressure tested. My next question would be; if the system is in fact low, then there should be a leak correct? An a/c system is a closed/sealed system right? Meaning you shouldn't have to add unless it leaked out? And If the system is full, then the switch on top on the accumulator is bad?

heyhar
September 5th, 2010, 18:02
Sounds like a good excuse to buy another tool! Gauges don't cost too much.......:eeks1:

sjx40250
September 5th, 2010, 20:13
Harbor Freight is your tool friend for this effort!

Yes it is closed. There is a diagnostic for checking the switch. You can disconnect and jump the wires and the compressor should run continuously. It will bypass the safety function of the switch, however.

First step is to check system pressures.

98NWCherokee
September 9th, 2010, 11:45
This sounds exactly like the situation I had with my 98. I tried replacing the low pressure switch and that didn't fix it. It ended up being corrosion on the back of the compressor clutch causing it to lose engagement when it got hot. I took off the clutch, sanded down the magnet, cleaned, lubed with locktight and re-assembled...AC has worked perfectly ever since.

sjx40250
September 9th, 2010, 12:39
On that note, 98NWCherokee, my 2000 GC compressor clutch was out of spec for the gap causing intermittant engagement. Lived with it for 2 years before finally fixing it by checking the gap against spec. Even thought about replaceing the compressor but at $500+ it was out of my range. I did replace the coil as the wires were perforated from someone else trying to figure out if there was power to the clutch.
Well checking the gap didn't fix it, reducing the gap did!

4wheel98cherokee
September 13th, 2010, 13:34
UPDATE:

My pressure cycling switch went out. I replaced it with a new one and my a/c is back on working perfect once again. Thank you guys for all of your support!:yelclap:

hoodride
September 14th, 2010, 11:55
On the switch you replaced, was it a matter of just swapping it out or is there oil/refrigerant pressurized behind it? Where I will have to get it refilled/recharged. Just wondering because a friend of mine's XJ is doing the same thing yours was.

CharlesS
September 14th, 2010, 13:30
The Low Pressure/Temperature switch screws on and beneath it is a schraeder valve to keep the refrigerant charge contained.

Charles

4wheel98cherokee
September 14th, 2010, 19:33
The Low Pressure/Temperature switch screws on and beneath it is a schraeder valve to keep the refrigerant charge contained.

Charles

What he said. It's seriously a 2 minute job and nothing comes out.