Adding Refrigerant without a Low Pressure fitting

Fred Munro munrof at
Sun Jul 6 11:03:20 PDT 2008

Ah yes, vague memories are starting to return... The older compressors had
this port. You have to be very careful adding refrigerant - if it goes in as
a liquid you can shatter the valves in the compressor...or at least that's
what I recall from the olden days when I owned a '91 200q. Unfortunately,
Audi omitted the dedicated low charge port from it's later models.

  -----Original Message-----
  From: Kneale Brownson [mailto:knealeski at]
  Sent: July 5, 2008 9:39 PM
  To: Fred Munro; mboucher70 at; quattro at
  Subject: RE: Adding Refrigerant without a Low Pressure fitting

  Link is to a pix of the Schrader valve on the front of the compressor
manifold on my 200q20v sedan.  It's the low pressure access:

  Fred Munro <munrof at> wrote:
    I believe the low pressure switch port contains a Schrader valve, so you
just unscrew the switch and screw on the adapter. You don't have to empty
the system.

    I've attached the post from Tom Green, the chap who found the adapter.


    I have broken the code on a/c charging through the low pressure
    switch port. This has been a sore
    point with lots of listers for a long time. So I decided that I
    must "carry a message to Garcia".
    I didn't have the problems Major Rowan encountered in carrying the
    President's message to General
    Garcia. It was as simple as reading Paul Waterloo's A8 posts on the
    correct way and poor man's way to
    recharge the a/c system. Please read both the posts, as they contain
    essential information for recharging
    the a/c system both by the correct factory method and the shortcut.
    I am not here to encourage you to
    recharge your system by either method. Unless you are confident in
    your ability and knowledge, take it
    to a professional. Otherwise, use at your own risk.
    There are follow on posts that show where Paul Waterloo sourced his
    I got mine at Midway Auto Supply. It is a FJC Air Conditioning
    Products R134a Tank Adapter --Part# 6016.
    I don't think a group buy can save over $2 unless there are a lot
    more interested than I know of.
    And, yes it works. It is a quick disconnect fitting, so if you are
    using old screw-on fittings for your refrigerant
    can or manifold, you will have to get adapters or a new hose set. I
    encourage all to use a gage set, but otherwise
    you are on your own.
      -----Original Message-----
      From: mboucher70 at [mailto:mboucher70 at]
      Sent: July 5, 2008 7:27 PM
      To: Kneale Brownson; Fred Munro; quattro at
      Subject: Adding Refrigerant without a Low Pressure fitting

      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

      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

      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

      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
        pressure switch port and use that as a low side fill, but it's a
        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
        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
        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
        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'
        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
        over-filled it by a factor of 3 (150 vs 45) and its still

        Any ideas?

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

        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
        (not a national consumer chain one, but one that services the local
        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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