[s-cars] Adding Freon to 1995 UrS6

[Jay M]

Tom,
 
Thank you Tom (and others) very much for the excellent information regarding evacuating and refilling my HVAC system with the proper amount of R134a. I think I have the info now to tackle the job safely and properly. Thanks again.
 
JM
 
From: trgreen at comcast.net
To: s-car-list at audifans.com; jaybird002 at msn.com
Subject: Re: [s-cars] Adding Freon to 1995 UrS6
Date: Sat, 7 Jul 2012 10:19:22 -0400

There are some lengthy threads that you may find here and on the quattroworld.com forum.  Also the Audiworld D2 A8 forum had good articles by Paul Warfield (??) a few years ago about topping off the system that is similar to the S6.  He had resisted putting it into a FAQ since it was lengthy and had to cover so many different possible problem areas.  I am of the same mind, and my thinking is perhaps I cankeep you from getting ripped-off by a shop, but to start from zero knowledge to advise you how to add refrigerant to your system is too difficult.  It also may not be in your best interest to do that.  That is why I don't think this stuff is suitable for any FAQ article.
If you are adding R134a to your system, that means it leaked out and moist air replaced it, so you have unwanted moisture in the system that forms a very nasty sludge when it combines with PAG oil.  Too much of this will clog the orifice tube (restrictor) and eventually other small tubes in the condenser and evaporator and really mess up the compressor.  Ok?  That is the total bad side of this issue.  If you are otherwise confident in your abilities, DIY work is no more difficult than other systems up to the point of charging the system.  You don't want to talk about pounds of refrigerant, but rather the 21.2 + 1.8/-0 ounces that fully charges the system.  This means the charging system needs to be very precise to measure the fill within one ounce.  All this is done with a recovery, recycling, recharging machine attached only to the high side port (the one you found on the right side of the condenser).
If you want to add a few ounces to the system from a 12 ounce can, you would have to do it through the low side by removing the low pressure switch under the plenum in front of the evaporator coil and using a R134a tank adapter or expensive a/c tool to allow you to quick-connect the can.  There is a schrader valve under the low pressure switch so removing it (and shorting the connectors so the compressor will run) will not allow any refrigerant to escape.  But, unless you modify the adapter, that schrader may prevent any freon from being added there.  That is the basics of the top-off procedure.  Just remember that that 12 ounce can contains more than half the full charge amount, and unless you use a guage set to monitor pressures you will probably overcharge the system.
The system pressure with the compressor off is about 100 psi so adding refrigerant through the low pressure side is only possible with the compressor running to draw down the low side pressure.  Adding the refrigerant through the high side is only possible with the compressor off, since those pressures with the compressor running are about 300 psi, and requires professional equipment.
Your DIY work, then, is only useful for replacing any parts required.  You still need a professional shop to evacuate and recharge the system.  
Tom '95 S6           '95.5 S6 avantKnoxville, TN
OnFriday July 6, 2012, at 8:43 PM,Jay M <jaybird002 at msn.com>  wrote:
Hello all, My 1995 S6 is blowing warm air when AC is on full blast. I hear the compressor working but air coming out of vents is not cold at all. I suspect the system needs a topping off of R134A freon. Although I have never charged the Audi S6 AC system with freon before I know on my other cars it is not a difficult task. The problem I have with the S6 is I can't determine where exactly the Low side port is located to attach my can of R134a. I did research and that indicates the S6 system holds about 1.7 pounds of Freon and should be filled to about 50 PSI on the low side when the ambient outside temp is 90 degrees. I looked and found an obvious and easily accessible port on the passenger side condensing unit located in front of the radiator but that seems too good to be true. I also found another port tucked away on driver side behind the radiaror. Can anybody tell me with 100% certainty where the low side port is located so I can attempt to recharge my AC system without bl
 owing up the can of R134A?  JM