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Old 07-04-2006, 08:56 PM   #1
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Default Air Conditioner Evaporator Freezes solid

Okay, I know its my fault for wanting to save a few bucks.

When my 97 SSE a/c failed this spring, my somewhat grumpy but "so-far-reliable" local mech says its not worth the money to, for example, replace a leaking evaporator.... that I couldn't expect much longer service from that, than from a cheapie "sealant" job.

So I opt for the sealant, away I go, it seems to work good.... until I go on a longer trip...

About 1/2 hour into the drive, the airflow into the cabin slows down to a trickle then to nothing...while the fan is howling... Turn off the A/c, and sure enough, the ice melts and the airflow starts up in a half minute or so.... turn the a/c back on, good for another half-hour.... (outside air temperatures about 29-32, and quite humid)

The 97'* a/c is the VDOT system which "...can match the air conditioning demands under all conditions without cycling.", whatever that means. This one has the "automatic" electronic control panel.

Crusty mechanic tells me that the pressures are within specs. Shop manual has some diagnostic stuff, but nothing about excessive evaporator ice-up.

Any hints???
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Old 07-04-2006, 09:07 PM   #2
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Sounds almost like the system is low... The Evaporator should not be turning into a block of ice... And the V5 compressor functions diffrently than the H6 compressor... The V5 is a variable unit and does not need to cycle off, the H6 has to cycle on and off as its not variable...

I wonder what he has the refrigerant charge at .... With my temps and humidity I had to have the low pressure side on mine read about 50-55 psi for the system to function properly...

When the Evaporator freezes up does the line to the reciever / drier freeze?

I am far from an expert on the AC system... So please don't beat me

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Old 07-05-2006, 12:33 AM   #3
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Yeah, I should have stopped and checked under the hood, but the freeze-up was so obvious from the airflow symptoms that I didn't bother.

Will have to go for another half-hour drive
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Old 07-05-2006, 03:23 PM   #4
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The 97 is the problem correct?

Proper low side pressure is around 50psi according to my 97 FSM ....however.. I could not find correct pressures listed clearly. I found only a section that stated if air temp was not good coming out of the vents and pressure is under 50psi that the system is probably low a pound of freon.

I have found most mechanics don't have the FSM'* and are running with general specs of 25-35psi as being a full system.
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Old 07-05-2006, 04:55 PM   #5
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Freeze-ups in my experience have been low pressure conditions. As stated, most commonly due to low refrigerant level. When the system is properly charged and operating, the surface of the coil stays above 32F, so freezing cannot occur.

If it'* freezing solid within 30 minutes, I'd have to put another pound in just for grins-n-giggles.

If the problem is caused by a line blockage restricting flow, this will not help.
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Old 07-05-2006, 05:14 PM   #6
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Honestly..Knowing what I mentioned about the if under 50 psi add a pound...I'd check the pressure and you'll probably find the mechanic "sweet spotted" it within the general 25-35psi spec.
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Old 07-06-2006, 04:13 AM   #7
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x2 on Frozen evap = low refrigerant. That'* pretty much universal to all freon-based refrigeration systems.
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Old 07-25-2006, 05:18 PM   #8
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Default UPDATE: Air Conditioner Evaporator Freezes Over

Quote:
Originally Posted by BillBoost37
Honestly..Knowing what I mentioned about the if under 50 psi add a pound...I'd check the pressure and you'll probably find the mechanic "sweet spotted" it within the general 25-35psi spec.
Not much significant progress....

Had a couple of trips where inside temperature control had to consist of periodic index finger on the "AC" button.

When system is running soon after start up, the pressures were about 255/55, and obvious good cooling happening. Disconnected the measuring device and went for a drive... came back after freeze up, and the pressures are about 250+ / 25... while watching for a while, the low--side pressure doesn't vary from 25.....

The complete Accumulator can, and the low side pipes where they are not insulated, are all coated in ice, solid.

This seems to point to a restriced/blocked Expansion (orifice) tube.... which I gather is fitted inside the pipe from the radiator/condenser to the evaporator, at that connection right close to the radiator / condenser, right????


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Old 07-25-2006, 05:32 PM   #9
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Default Re: UPDATE: Air Conditioner Evaporator Freezes Over

Quote:
Originally Posted by Icebound
This seems to point to a restriced/blocked Expansion (orifice) tube.... which I gather is fitted inside the pipe from the radiator/condenser to the evaporator, at that connection right close to the radiator / condenser, right????
Correct and yes.

Most specifically, the orifice tube/filter is located in the expanded portion of the liquid line. You'll see the worked part of the tube meant to hold it in place.

Your A/C system sealing gunk (and I'm being nice there... ) likely clogged up your orifice tube but good. Now you have to open the system to replace that tube and screen. If you do that, you should (at the very least) have your grumpy mechanic friend pull a vacuum on that system for 24 hours to dry out the accumulator dessicant. Then seal it up pronto. Either that or you'll have to replace the accumulator assembly also.
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