[s-cars] Re Adding Low Pressure to AC

[Tom Green]

>
That description of "add a low pressure port" sounds like cut the  
tubing and install a new fitting in an appropriate place?  I would  
want someone who is a master at thin aluminum tubing welding to
add this port, and sounds unnecessarily expensive to me.  Although a  
home or commercial shop would do that type of work all the time, you  
don't usually see that kind of work done at an automotive
AC shop.    Perhaps they are just using the low pressure port under  
the low pressure switch next to the AC evaporator.

A quality AC shop will use a recovery machine to evacuate the  
refrigerant before opening the system to replace any o-rings at  
leaking connections, replace the orifice tube, and any other work.   
Then if the system holds pressure and vacuum, replace the refrigerant  
by measuring the weight of refrigerant installed through the high  
pressure port on the condenser.  Most will probably just guess at the  
refrigerant oil needed unless major components are changed.   Most of  
the DIY cans contain a small amount of make-up oil with the R134a.

The issue is measuring the duct temperature after the job is done.  If  
it is not within specs, i.e., doesn't cool the passengers adequately,  
they may have to tweak the charge with another ounce or
two of refrigerant.  This is where the low pressure port comes into to  
play since you can add that two ounces there with the system running  
to adjust the duct temp just like the DIY guy would have done without  
checking out the system.  Having both ports available can help  
diagnose problems by connecting a manifold gage set and observing the  
system pressure balance while it is operating.

With a well maintained system and good equipment to measure the  
refrigerant charge, just the high pressure port will work fine, but  
you have to get the charge just right the first time.  The added labor  
tweaking the system on a fixed price job is probably the reason some  
of the shops declined to charge the system.

Plus, we are a bunch of DIY guys anyway.

Tom

			

> -----Original Message-----
> Date: Tue, 26 May 2009 15:54:23 -0700 (PDT)
> From: Gregory Wolters <gjwarch at sbcglobal.net>
> Subject: [s-cars] 94 S4, Adding Low Pressure to AC
> To: S-CAR-List at audifans.com
> Message-ID: <123288.61375.qm at web83303.mail.sp1.yahoo.com>
> Content-Type: text/plain; charset=us-ascii
>
> Hi All,
>
> My S4 seems to need to have the AC recharged.  A friend recommended  
> an AC shop to do it.  I think I can save money over the Audi shop I  
> usually use.  I called them to see if they were familiar with  
> Audis.  I've been to a couple of shops that couldn't charge because  
> of the absence of a low pressure port on the AC.
>
> They said that on Audis, they add a low pressure port to do the  
> recharge.  He said this isn't a problem.  I asked about potential  
> for leaks and he said it would be fine.
>
> Does anyone have experience with this issue?
>
> Thanks,
>
> Greg
> 94 S4
> 95.5 S6