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Discussion Starter #1
This is the latest chapter in the story of my haunted 98SE...

So I'm on a long trip last week in moderately hot weather, running the AC on "high" and "max AC", and after awhile, the airflow coming through the vents, while apparently cold, is not what it used to be.

Remembering back to an old trick that we used at an old gas station that I worked where the roof-mounted AC unit would freeze up, I switched from "max AC" to "vent". After a few minutes, the air flow returned to normal. I switched back to "max AC", and life was good until it froze up again. Now I've got to go back and forth every so often.

This happens on all fan and both AC settings. Any idea as to what's going on and how I might be able to fix it?

Many thanks in advance,
Sean, owner of the haunted 98SE
 

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You shouldn't use "max A/C" all of the time anyway. "Max A/C" is the same as normal, but it just recirculates the air inside the car (no outside air entering). It's not as efficient because you are trying to cool down air that at some point is as cool as it's going to get. On real hot and humid days it will most likely freeze up. The best thing to do is to use "max A/C" until it is cool in the car, then switch to normal. If the normal setting doesn't keep it cool, then you may need to add some charge to the system. Freezing is sometimes a sign of an under charged system (but not always). My parent's 86' Bronco II used to freeze up even on normal A/C and it wasn't under charged.

Have the system checked to make sure everything is straight.
 

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The Evaporator is freezing up.

I would put my money on the Clutch Cycle Pressure Switch then a low charge since it's R-134a.
 

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Originally posted by NateNBeckie@Jun 2 2004, 10:20 AM
You shouldn't use "max A/C" all of the time anyway. "Max A/C" is the same as normal, but it just recirculates the air inside the car (no outside air entering). It's not as efficient because you are trying to cool down air that at some point is as cool as it's going to get. On real hot and humid days it will most likely freeze up. The best thing to do is to use "max A/C" until it is cool in the car, then switch to normal. If the normal setting doesn't keep it cool, then you may need to add some charge to the system. Freezing is sometimes a sign of an under charged system (but not always). My parent's 86' Bronco II used to freeze up even on normal A/C and it wasn't under charged.

Have the system checked to make sure everything is straight.
Max A/C is better to use on humid days to prevent freezing. Since the air is recirculating, more moisture is kept out of the air. When fresh air is drawn in, so is fresh moisture, which can accumulate and freeze up your evaporator.
 

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no way this is a low charge

a low charge will never get cold and the Compressor will cycle quick.

I would bet on the the Low pressure switch Like JJ57 said.
 

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it is the switch,the switch is there to prevent the freeze up of the evaporator,normally it sits on top of the accumulator.or you have way too much r 34a in the system,hook up the guages and see if the ac clutch is engaging :banana:
 

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The cycle switch switch is on the Suction or Low Pressure side, usually on the accumulator or Low Side line.

A low charge would result in a rapid cycle of the compressor, and little to no cooling. An overcharge would result in a high discharge pressure, and not much cool air at all.
 

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Discussion Starter #9
Thanks for the replies, everyone...

It's a good thing I like this car as much as I do, because this hodge-podge of constant tail-chasing is getting old... lol.

Here's a brief recollection of my recent troubles...

1. Last August, the compressor clutch failed. Replaced it, but had to remove compressor to do it. Recharged system. Blew ice-cold, but not for long.

2. Realized that I should have replaced the accumulator/drier at the time I removed the compressor. Did that in February. Had system recharged. Blew ice-cold, but not for long (like less than a week).

3. Took the car to shop #1 in March, who advised me that the condensor, compressor, and high-pressure lines (supposedely they were full of leaks) needed to be replaced for about $1,500. Didn't believe them for a minute, so took the car to shop #2. They told me that the seal between the pressure switch and the drier was ruptured (prolly when I reinstalled the drier). They replaced the seal, recharged the system for $150. Blew ice-cold until the freezing symptoms appeared. Now it blows ice-cold when it's not frozen.

So, I reckon the cycle sensor is something that the system has to be discharged and recharged again to replace. Just damn... I'll post the results...

Thanks again,
Sean
 

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Originally posted by sablerider@Jun 2 2004, 06:23 PM
no way this is a low charge

a low charge will never get cold and the Compressor will cycle quick.

Study refrigeration basics again. A "low" charge will freeze the evaporator coil, especially if it's cooling humid air. A "real low" charge will rapid-cycle the Low Pressure switch.
 

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We are dealing with R-134a in a vehicle, not R-12, R-22 or R-502 in a chiller/central unit.

A Vehicle A/C system will rapid cycle for a low charge. There would not be enough time to freeze the evaporator up with R-134a and cycle like that. It has to be stuck closed or at a lower pressure (well below the cut off maybe 15psi) to freeze up.
 

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One thing that has been overlooked is the evaporator drain. Is it working like it should? Is there a puddle of water under or next to the RF tire? Any accumulation of water that does not drain will freeze up the evaporator in time.
Good Luck
Bill
 
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