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  #1  
Old 09-02-2014, 08:19 PM
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'94 JGC unusual AC problem

Iíve been reading about problems with the AC fan working only on high, but have yet to find a descripton of the problem Iím now having on my 94 JC Laredo, 5.2: when I start the car, the AC fan works fine, on all speeds. But on a long drive, after about 45 minutes, the output from the vents begins to decrease, and finally ceases. The FAN never stops, but the output to the vents is blocked . . . and not just to the AC vents, but to the floor vents and the defroster as well. If I turn off the AC completely, wait about 10 minutes, and turn it back on, I again have fully functional air - - but now the gradual shut-off happens faster.

Again, the fan never stops, but the output does! And this is the case on all fan speeds.

I was thinking about trying to change the blower resistor, but that doesnít sound like it will solve this problem.

Thanks in advance for any help!
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  #2  
Old 09-02-2014, 08:47 PM
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Re: '94 JGC unusual AC problem

Not familiar with the ZJ AC system. But indeed, if the fan continues making its normal noise, i would not expect that the resistor is the problem.
I expect that the evaporator is freezing closed, so that no air can pass anymore. Waiting 10 minutes with the air off will let the ice melt and the problem is gone. I expect that the ZJ uses an AC pressure switch, which should switch the compressor off at a certain pressure and which should prevent the freezing of the evaporator.
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Old 09-03-2014, 01:38 PM
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Re: '94 JGC unusual AC problem

If you set the AC to recirc mode and max fan, does it sound like a jet engine [it should]

Are you saying the fan noise never changes?

Even if the evap is frozen, you should get air.

Do you have the ATC, such that you can run diags against the A/C system to check all the doors, actuators, etc?

If you have a mechanic's light tube/viewer, on the passenger side you can pull the door off and have a peek in there to see if the evap is frozen over. You could also give it a shot of very hot water--after making sure you don't have a plugged drain.

Does the unit leak water all over the place after you shut it off when the air stops?
Or do you have a plugged drain, where you pretty much have to get under the thing since it drains into a frame hole....
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Old 09-03-2014, 04:47 PM
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Re: '94 JGC unusual AC problem

Is the ZJ AC system different then that from the WJ? Is not all air going through the evaporator first? As by my knowledge all airflow will stop as soon as the evaporator is frozen closed.
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Old 09-03-2014, 04:59 PM
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Re: '94 JGC unusual AC problem

Quote:
Originally Posted by Frango100 View Post
Is the ZJ AC system different then that from the WJ? Is not all air going through the evaporator first? As by my knowledge all airflow will stop as soon as the evaporator is frozen closed.
Don't know the WJ system.
Had evap freeze on a 95 ZJ, but some cold air still made it out, ATC variant of system.

It is still a strong suspect, where a mechanic scope down the side access might be able to see it.
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Old 09-03-2014, 06:36 PM
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Re: '94 JGC unusual AC problem

It is probably wise to check if the AC compressor cycles on and off regulary and doesnīt stay on all the time. A faulty AC low pressure switch could be the problem. This switch should switch the compressor off and prevent the evaporator from freezing. This switch sits most probably on top of the accumulator.
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Old 09-03-2014, 09:38 PM
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Re: '94 JGC unusual AC problem

Thanks for the great replies.

So far Iím thinking that the evaporator freezing over is the likeliest problem. Itís only happened when Iíve had the AC on its highest setting and, and the fact that the output gradually diminishes leads me to believe that itís icing over. Also, my mechanic serviced the AC earlier in the summer Ė we thought it needed Freon, but turned out it was fully charged - and the problem was that the compressor was turning on but not staying on for a full cycle. I suspect that in fixing this problem, my mechanic may have bypassed the AC pressure switch, whether accidentally or on purpose. Iíll certainly ask him!
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Old 09-03-2014, 09:48 PM
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Re: '94 JGC unusual AC problem

Ok, let us know what the solution is.
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