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Clogged Evap? Diagnosis check, pls.

fasto on Sun May 03, 2009 12:49 PM User is offline

Year: 1993
Make: VW
Model: Corrado
Engine Size: 2.8
Refrigerant Type: R134
Ambient Temp: 60
Pressure Low: 26
Pressure High: 135
Country of Origin: United States

Had a little trouble with this:

Last year with the help of AMA I replaced the compressor & condenser on this car, and had great AC performance (well, great for a euro car..).

This spring, went to check, and had little to no cooling. Evacuated system, was down about 300 grams (out of 1000 grams total charge). Found the TXV had a slow leak, so I replaced this (with an AMA part). Vacuumed & recharged to 1000 grams, and the system pressures look GREAT (26/135 @ 65F). But, still no cooling...

I suspected reheating, so I bypassed the heater core... still no cooling.

I checked the temperature of the piping in & out of the evap, was about 38-40 degrees checked with a thermocouple. Something is getting cold, as it should with 26 PSI low side.

I pulled out the blower resistor which lets me get the thermocouple right into the evap matrix.. what the.. 70 degrees??? With the blower fan not running?

The only thing I can think of is that the evap with is a sort-of parallel flow unit

has at least some clogged tubes. Why is a mystery. I haven't had a catastrophoic compressor failure, ever. I've had 2 bad refrigerant control valves which required compressor replacement, and two leaky TXV's. The system has never been totally empty. Who knows.. it is 17 years old.

Sooo... is my though along the right lines, that the evap is no good? I can't think of anything else.

Oh, I can't say enough good things about the Mastercool Professional manifold set. The screw-down R134 service adaptors are the bomb. Why I didn't get one of these first is beyond me...

Thanks, Aaron

TRB on Sun May 03, 2009 7:17 PM User is offlineView users profile

Not counting it out but I doubt you would have circulation with a T & F core if it were plugged!

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fasto on Sun May 03, 2009 7:22 PM User is offline

This evap has four (I think) paralleled loops for the refrigerant to pass through - If 2 or 3 were clogged one would still be open, allowing flow, I'd think.

I could only reach the top section with the thermocouple easily then it started raining. I guess I can check the other areas of the evap in a few days.
Thanks,
Aaron

TRB on Sun May 03, 2009 7:32 PM User is offlineView users profile

That would be true if the core has a looped style flow. Might try and get a IF thermometer and see if you can get some readings on the return tubes. But if you have not had a compressor or drier failure? What is going to be in the system to clog the core?

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Contact: ACKits.com

fasto on Sun May 03, 2009 10:57 PM User is offline

Quote
Originally posted by: TRB
But if you have not had a compressor or drier failure? What is going to be in the system to clog the core?

I haven't had a compressor failure, other than a stuck RCV. I don't think I've had a drier failure, as the TXV I replaced was pretty clean and did not have any "sand" inside it, nor did the high pressure line. There was a little light grey stuff, probably aluminum dust, in the oil; I have seen this before and I don't think it's serious - and it certainly couldn't clog the evaporator. What I could see of the evaporator through the fan resistor hole looked in good shape, and I'm pretty good with the inspection mirror after working on airplanes for a number of years. I didn't see any green stains, powdery spots, or anything else unusual - a few dried up leaves, that's all.

That said, I can't understand why the temperature is 70 degress, with the engine bay side inlet pipe & outlet pipe measured at 40 degrees. ??? I have no idea, other than something's wrong with the evaporator in some way. What else could be going on? I'm at my wits end... If it wasn't a 6 or 7 hour job to R&R the evaporator I'd take it out just to inspect it. I don't think that I can get any thermometer onto the suction lines as they're all inside the evap case except for the two connections sticking out into the engine bay. I will try to check this as soon as I can. I don't that flushing this evap would be successful given its design.

Since my first note, I saw one other thing that might support a clog somewhere. I saw a couple times where the high side suddenly went to 400+ PSI for an instant before the overpressure switch shut the compressor down, this happened twice over a few hours of testing. The condenser wasn't anything like hot enough to have that temperature, I think that's over 180 degrees! I did not see the low side when the spikes ocurred. The last spike seems to have permanently tripped the overpressure switch, so I am out of action until I can get another three-way switch.

HECAT on Mon May 04, 2009 10:28 AM User is offline

2 compressors, 2 TXV's, and one condenser; you may not have a debris issue, but you may have a serious oil overcharge.

How much oil has been added with each service procedure? What is the total amount of oil in there now?

If the TXV can be removed without tearing out of the dash, and the evaporator is not a leaker; it can be flushed where it is. Understanding the "parallel paths" of the various designs is the key to success, not a reason to throw in the towel

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fasto on Tue May 05, 2009 6:01 PM User is offline

I appreciate all your comments, guys.

Quote
Originally posted by: HECAT
2 compressors, 2 TXV's, and one condenser; you may not have a debris issue, but you may have a serious oil overcharge.
How much oil has been added with each service procedure? What is the total amount of oil in there now?

Last summer, we started clean with a new compressor, new condenser, new receiver/drier, new TXV, and all lines drained & blown clean with the lines out of the car. Shipping oil was drained from the compressor. The amounts of oil recommended in the sevice manual were added to each new component; the evap was not changed and the amount of oil it contained (as suggested by the service manual) was subtracted from the total oil charge. The evap fittings were taped over while the remainder of the service was underway
Last weekend, the TXV was changed, no oil was lost and no oil was added.

Quote

If the TXV can be removed without tearing out of the dash, and the evaporator is not a leaker; it can be flushed where it is. Understanding the "parallel paths" of the various designs is the key to success, not a reason to throw in the towel

The TXV is simple to remove as it's in the engine bay. The evap does not seem to be a leaker; I examined the side facing the blower with an inspection mirror & light without seeing any trace of green dye, aluminum corrosion, or any other nonsense. There is no trace of dye in the evap drain tubing. The air discharge side is of course inaccessable, as it's facing inside the air handling ductwork.

Would the flusing system that you manufacture be sufficient to flush this evap? You can see from the picture that it's got 4 loops arranged horizontally. Installed in the car, the evap is rotated 1/4 turn counterclockwise from the picture.

My concern is that some sort of corrosion has disbonded the fins from the tubing, and while the tubing is getting cold the fins are not, thus the 70F readings while the inlet tubing and outlet tubing read 38-40F.

If it ever stops raining here I will attempt to measure the temperature of the 4 suction lines in front of the internal manifold (visible in the picture). We are supposed to get rain for the next 10 days, though.

With a new evap costing about $100 and taking "only" 6 hours to put in I admit that I am leaning towards this solution.

HECAT on Wed May 06, 2009 5:59 AM User is offline

Quote
Originally posted by: fasto


Would the flusing system that you manufacture be sufficient to flush this evap? You can see from the picture that it's got 4 loops arranged horizontally. Installed in the car, the evap is rotated 1/4 turn counterclockwise from the picture.

Yes, the process is much more capable than most any other method at cleaning parallel paths; this is a parallel tube and fin circuit. Just blowing, spraying, soaking, or simple circulating can and will take "the path of least resistance" around a blockage if it does exist. Our Pulsating method introduces a solvent cleaner with high velocity and a kinetic energy pulse than can and will scrub and clean the multiple parallel paths. External corrosion (fin separation) or blocked air flow may be an issue, but I find it hard to believe the evap is blocked internally unless a sealer has been used. Keep in mind that any debris or contamination that can enter the evap must first pass through the orifice of the TXV.


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