Adding Refrigerant without a Low Pressure fitting

mboucher70 at mboucher70 at
Sat Jul 5 16:27:18 PDT 2008

Kneale, I've got a good sense that mine doesn't have a low pressure fitting.  Just to be certain, can you help me locate where it would be on yours?  The "front of the return manifold on the compressor"...if I recall the compressor is below the radiator, out of sight.  Would I be able to see the black capped low pressure fitting on your 200q20vs from the same vantage point that I could see the white capped high pressure fitting?  Or would I need to be under the car to see it?

Fred, in order to add the low pressure adapter to a car that doesn't have one, I'm assuming that you'd need to first empty the system of existing coolant?

I'm wondering if its possible to add refrigerant via the high pressure fitting, with the car turned off.  I figured that the aerosol can is probably pressurized enough to overcome the 60psi and get at least some refrigerant in, but it surely won't overcome the 150psi present when the a/c is on.  I appreciate that I'll get a lot smaller fraction of the can into the car via the high pressure valve at 60psi than via the low pressure at 30-50.  The only impact of this is that I'll require more cans.  Anyone see a flaw with this?

----- Original Message ----- 
From: Kneale Brownson 
To: Fred Munro ; mboucher70 at ; quattro at 
Sent: Saturday, July 05, 2008 5:38 PM
Subject: RE: How to Determine if your Audi is Actually Short of Refrigerant

On my 200q20vs, there's a low pressure fitting on the front of the return manifold on the compressor.  Black cap.  That's where I've put in refrigerant.

Fred Munro <munrof at> wrote:
  You've connected to the high side adapter, as indicated by the lower
  pressure when the compressor cycles off.

  From what I recall Audi doesn't provide a traditional low side fill
  connection. I believe you can get an adapter that will fit on the low
  pressure switch port and use that as a low side fill, but it's a weird
  thread. One of the guys on the UrS list found a source of these adapters and
  was supplying them to the list.


  Fred Munro
  '97 S6

  -----Original Message-----
  From: quattro-bounces at
  [mailto:quattro-bounces at]On Behalf Of mboucher70 at
  Sent: July 5, 2008 4:26 PM
  To: quattro at
  Subject: Re: How to Determine if your Audi is Actually Short of

  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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