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Evaporator Flush

arivera102 on Sun October 25, 2009 9:34 PM User is offline

Year: 1998
Make: Volkswagen
Model: Beetle
Engine Size: 2.0
Refrigerant Type: r134
Country of Origin: United States

Yesterday I had my local auto store run an AC diagnostic because my AC lines were freezing up and my AC was blowing warm air. They told me that I had to replace the
Evaporator because it was freezing up and backing up into the lines. Now my questions is, Do I need to replace the Evaporator? or
could I take it to an AC specialist to have it flushed?

Your help is greatly appreciated.


HECAT on Mon October 26, 2009 6:09 AM User is offline

Without specific test data, it is difficult to comment. If you failed to understand or relay the technical info to us, that is OK. If they clearly stated the evap was the cause of freezing, I would recommend another shop.

IMHO. It is not the evaporator; something is causing (low charge, defective thermal controls, etc) the evap to freeze up. However, if a faulty device (TXV, etc.) is the culprit and buried behind the dash with the evap, then replacement of the evap could be prudent; since it is over 10 yrs old and you are already paying the labor to access it with the service a faulty thermal control.


HECAT: You support the Forum when you consider for your a/c parts.


arivera102 on Mon October 26, 2009 8:46 AM User is offline

That could be the problem. I had a new AC compressor installed last Tuesday and the guy that did the work didn't change the Drier or Expansion Valve (he said it was not needed). I think he didn't want to go through the trouble of replacing it (he was a freelance mechanic). That's what happens when you don't have a lot of money to take the car to a repair shop (I'm currently unemployed). Should I take it to a shop and have them replace the drier and expansion valve?

mk378 on Mon October 26, 2009 10:26 AM User is offline

It's a SD7V16 variable compressor system. Freeze-up is avoided by the compressor controlling the low side pressure. An evaporator temperature sensor is not necessary.

Either the new compressor is not working properly, or your mechanic did not pump out the air from the lines before charging. A mixture of air and refrigerant will allow freezing (and other problems) even though the compressor is OK.

System pressures need to be measured to diagnose. If the low side is running below 20 psig, the compressor isn't varying properly. If it's staying in the 20's yet freezing up, I'd strongly suspect air in the lines.

Or you could start by replacing the drier (really must be done on any major service) and evacuate and recharge properly and see if the problem still occurs.

iceman2555 on Mon October 26, 2009 11:24 AM User is offlineView users profile

The process of the compressor 'varying' in displacement is directly related to the 'signal' from the TXV.
Since the system was not repaired properly from the drier (could be a restriction) and new TXV (again a possible restriction) there are numerous variables in this repair.
Was the system evac'd correctly (air as mk378 states) or as the system charged correctly (no gauges....the correct recharge equipment) as HECAT stated.
It would be a stretch of the diagnosis procedure to state the evap was the root cause....could be...but my first steps would be to bring the system back to a base line....recover, flush, NEW TXV, NEW Rec/Drier/Filter and the correct evac and recharge procedure. This procedure would bring the system back to a point where all temp control devices (compressor control valve ) could be properly evaluated.

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

TRB on Mon October 26, 2009 11:33 AM User is offlineView users profile

Note: There is a bad batch of expansion valves for this vehicle being sold by various suppliers.


When considering your next auto A/C purchase, please consider the site that supports you:

Edited: Mon October 26, 2009 at 11:34 AM by TRB

iceman2555 on Mon October 26, 2009 3:14 PM User is offlineView users profile

TRB, that is certainly true...encountered this problem during the summer with two different vehicles. One located in the St. Louis area and the other Northern CA. Both had had multiple 'kits' installed, including TXV's. Both exhibited low cooling performance, low side pressures were, what would be deemed acceptable, high side pressures were low and, of course, low cooling performance.
The issue with TXV's is that when the valve does not function properly, the reference signal to the control valve 'mis reads' this signal and adjust according. In some instances, the pressures will modulate up and down as the compressor control valve seeks a valid signal from the TXV.
Often when the system is overcharged the problem maybe rectified, however on both of these units the problem remained.
Adding 2-4 oz of refrigerant to the system would result in a return to normal system operations, the pressures were acceptable and vent cooling performance was restored. However, after app 5-8 minutes the system would return to the same conditions, low side acceptable, high side low and very poor cooling performance. The time element is app the time it takes for a system to stabilize after adding refrigerant.
This is not an un common problem with other mfg'ers variable compressors.
Replacement of the TXV solved the problem. No more new compressors for the junk pile....satisfied customer and perhaps a installer and jobber that learned a lesson...."It is not always the compressor!"

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

arivera102 on Tue October 27, 2009 2:43 PM User is offline

Okay, here's what the AC mechanic told me after run test on the system. He said the Drier is clogged up. The only problem is that the hex screw that
is connects the condenser to the drier is stripped and he can't take it out. Any suggestions?

iceman2555 on Tue October 27, 2009 10:13 PM User is offlineView users profile

Is this the same 'mech' that stated earlier that the evap was freezing up?
The drier could be restricted from debris from the previous compressor......remember someone talked about flushing the system....there is a reason for all this 'extra' stuff.....considering that the connector is stripped (curious about that statement) and there is a possibility of debris formulations within the inlet side of the condenser (again from the previous compressor failure), a suggestion would be to replace both the rec/drier/filter and the condenser. There are tools in the market to repair damaged threads on a condenser but considering all issues....replace the darn thing.
Be sure to flush the system (evap and lines) during the repair process.
Once more, suggest to replace the TXV (OE unit preferred), there is a possibility of debris formulations within the TXV also. A restriction here may result in serious compressor damage due to lack of lubricant flow and also may result in loss of cooling system performance.

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

bohica2xo on Wed October 28, 2009 2:03 AM User is offline

With the work that has been done it is hard to say where this started. Typically a low charge or defective control valve leads to the compressor replacement, and the issues begin there when someone unfamilar with the variable displacment system can't seem to get it charged again.

On a 10+ year old system the dryer should have been replaced when a compressor was replaced. It has done it's job, and is a 20 dollar part.

The dryer on that car is connected with a "peanut fitting", which in this case uses a recessed bolt. It sounds like someone used the wrong tool on the bolt head, and now it is not removable with standard tools. There are tools that would grip the remains of the head in some instances, or you can just drill it out. The good news is that the bolt threads into the dryer you are going to discard, so you can just drill it with the same size drill as the bolt shank - if you damage the dryer it is going in the trash anyway.

The TXV on that car is easily accesible under the hood. It is bolted to the firewall on the passenger side. If it does indeed need to be replaced, it is not labor intensive.

I still question the diagnosis. I would be inclined to flush the system, replace the dryer, and then charge it with the proper charge of oil & refrigerant for testing & evaluation.

Given the compressor replacement, damaged fasteners, unknown system oil quantities etc., it is time to go back to square one.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

arivera102 on Thu October 29, 2009 5:38 PM User is offline

Here's the latest update on my car. I found a new mechanic that's ASE certified that looked at my AC. He said that the person that was trying to remove the Drier broke the line from
the condenser. He needs to replace the condenser and Drier, for that he needs to remove the front of the car to replace the condenser. He also told me that he will flush the system
and recharge it. I hope it doesn't cost me an arm and a leg, I'm currently living off unemployment. Do you have any idea how much will cost?


mk378 on Thu October 29, 2009 6:29 PM User is offline

Get a written estimate before any major work like that.

But he's on the right track, sounds like the car does need major work. I think you do have to take the whole front off of a New Beetle to do a lot of things, like change the headlight bulbs.

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