134a conversion, High and Low pressure readings

[TooManyAudis at aol.com]

I don't think that 250 on the high side is out of bounds for a 134-A  Car.  
If I recall correctly, something over 300 or 350 will set off the  high 
pressure switch.  your climate control diagnostics will tell you if  the high 
pressure switch is tripped, and how many times since it's been reset,  etc.

 
I think normal low side is between 25 to 40.  What is most important  is that 
the compressor continues to run -- if the low side isn't too low, or the  
high side isn't too high, you should cool just fine.  Best I've gotten on  my 91 
200q is 45 or so from the vents.  takes a few minutes to cool, but it  does 
just fine.  My 88 80q will do 40 or so.
 
Regarding high side pressure, the fan should kick into high speed around  
250.  that should lower the high side pressure by a few pounds.  if  this is not 
happening, check the switch.  Jump it, etc to narrow down the  problem.
 
The most likely cause for excessive high side pressure on these units is  a 
clogged orifice valve.  This should have been changed with the  conversion, 
along with your drier.  If not, I'm willing to bet that your  high side pressure 
will get higher and higher soon.  
 
they sell a standard orifice (expansion) valve for around $5 at your  local 
FLAPS.  There is also a variable valve that is optimized for use in  134-a 
converted cars.  I have this in my car now.  It didn't make a  bit of difference 
over the standard valve.   Don't waste your  money.
 
 
-- Tom
 

-----Original Message-----
From:  quattro-bounces+tm2=zipcon.net at audifans.com
[mailto:quattro-bounces+tm2=zipcon.net at audifans.com]On  Behalf Of
Huppert, Eric
Sent: Tuesday, July 12, 2005 8:31 AM
To:  'quattro at audifans.com'
Subject: 134a conversion, High and Low pressure  readings


Gentlemen,

Difficult patient: 90 Audi  200TQ

After numerous issues with the AC system I'm getting fairly close  to cold
air, versus cooler air!

Of course I only have R12 gauges, and  have had fairly little luck finding a
134 pressure chart similar to the R12  charts which were relatively common
back when I was turning a wrench for a  living. And my vacuum pump will only
pull about 28", which I know isn't  really enough...

System calls for 1000 grams R12. All the info I've found  on 12 to 134
conversion states start with 70-80% 134. Charged with two cans,  apx 680g and
high side is over 250lbs (above idle) Ambient temperature was  apx 85F...
Press seems high? Vent temp was around 50F.... As for low  pressure, need to
get 134 adapter to hook up to low port!

Thoughts,  guesstimates on apx hi/low pressure figures????

Thanks, Eric