[s-cars] FW: A/C DIY 134a recharge

[Djdawson2 at aol.com]

In a message dated 6/7/2004 9:12:29 PM Mountain Daylight Time, 
tr0910 at softhome.net writes:

> Well now its my turn and I have the juice, if I can just figure out a
> way to get it in there.  Does everyone still agree it can't be done by
> the shadetree mechanic??
> 



Tim,
To answer your question...  If you've got a can of 134, and nothing else, 
chances are good that the answer is no.  Here's why:

When your system is running (engine on, compressor engaged) the typical 
pressures on your system will be roughly 20 psi on the low side (compressor inlet) 
and around 250+psi on the high side (compressor outlet).  Hook up a can of 134 
to your high side (the only port available on 134 S4's) and it may explode.  
You can't charge your system because the pressure in the can is less than the 
port pressure.

If you were to shut the system down... engine off... the system pressure will 
equalize.  What I have typically seen on a shut down system is 60-80 psi.  
This affords you some opportunity, but is somewhat risky.  You could, 
theoretically, get the 134 out of the can and into your system by heating the can enough 
to generate internal pressure that exceeds the system pressure.  Me... I 
wouldn't do it for several reasons.  1st, it isn't exactly a safe approach.  2nd, 
you have no idea how much your system needs.  If you have gauges, you could 
add a little, hook up the gauge and engage the system, and keep going until 
you've reached a reasonable high side pressure reading... or quit when the cooling 
output is adequate.  This still isn't a great approach, since you will be 
introducing considerable air into the system with repeated hooking up of the can, 
then the gauge, then the can, etc...  Further, you aren't able to see a low 
side reading, which is an important part of the equation.  Finally, Audi hasn't 
provided us with a sight glass, which further confuses the charging task.

IMO, the best solution for the shadetree mechanic, is to take your car into a 
good A/C shop and have a low side port added to the system.  This will 
obviously involve opening your system up.  Once the port is added, replace the 
receiver/dryer, and have the system evacuated and recharged.  This doesn't save you 
any money now, but would at least get you ready for the next time.  And there 
will likely be a next time... as you must be leaking somewhere. And through 
your new low side port, you can charge as you need to in the future.

HTH,
Dave (A/C certified, believe it or not) in CO