How to Determine if your Audi is Actually Short of Refrigerant

Kneale Brownson knealeski at
Sat Jul 5 14:35:32 PDT 2008

That's a high pressure port.  That hose from the pump to the condenser will be the one with the most pressure on it.  That port should have a white or gray cap on it.
  On the front of the manifold on the compressor where the return line from the evaporator box connects, there should be another schrader valve with, usually, a black cap.  That's a low pressure port that I use for filling.
  Bentley says the high pressure valve opens at between 153 and 217 psi and closes at between 190 and 253 psi.  I interpret this to mean your measurement is reading low.
  The low side switch opens at between 11 and 16 psi and closes at between 33 and 42 psi.
mboucher70 at wrote:
  It turns out that Duracool is packaged with a gauge for measuring the 
refrigerant pressure, as well as high-side and low side adapters if you need 
them. I picked up a package today and followed the instructions to measure 
the low side pressure. The gauge is color coded and indicates, the 
following ranges:

0-25psi: low (green)
25-45psi: filled (blue)
45-65psi: alert (yellow)
over 65: warning (red)

I fitted the low side adapter, started the engine and turned the AC on, let 
it run a few minutes, and atached the gauge. To my surprise, the pressure 
read 155psi, dropping to 150 when the compressor cycled off. When the AC 
and the car were shut off, the pressure slowly dropped to about 70psi, and 
never went below.

Car is an Audi 100 1990. The adapter that I'm using is labelled as the low 
pressure adapter. I'm connecting to the only visible 'filling' adapter, 
which is mounted in front of the AC/radiator, just behind the driver's side 
headlight bulb.

Car was bought 9 years ago, used. It is original R12 (no conversion). No 
refrigerant has been added since I bought it. Is it possible that someone 
over-filled it by a factor of 3 (150 vs 45) and its still functional?

Any ideas?

----- Original Message ----- 
Sent: Thursday, July 03, 2008 7:03 AM
Subject: Re: How to Determine if your Audi is Actually Short of Refrigerant

mboucher70 wrote:
> Short of taking a car to an AC shop, what is a good method to determine if
> its actually short of refrigerant?

I bought the gauges needed to test the AC from my local auto parts place
(not a national consumer chain one, but one that services the local trade).
It cost about $100. You can get a cheaper one at Harbor Freight:

Kent McLean
'99 A4 Avant
'91 200 Avant
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