Adding Refrigerant without a Low Pressure fitting

Kneale Brownson knealeski at
Sat Jul 5 17:40:38 PDT 2008

On my 200q20vs, the low pressure valve is right on the front of the square manifold that's to the outside (toward the wheel) of the compressor.  The return line goes into the back of that fixture and the valve is on the front of it.  You have to be at an eyelevel just below the bottom of the front bumper cover to see the valve.  I use a hoist, but I've serviced the A/C on the cement pad outside my barn by lying on the ground to attach my gauge set to the valve.  I've never attempted to put refrigerant into the high side of a system.  The process is hook up to the low side valve (I'm sure there's one somewhere in every system) and let the compressor suck the refrigerant out of its container until the specified level is indicated on the gauges.  The Bentley uses the same A/C components schematic for all the '89-'91 100 and 200 models, and that schematic shows a low pressure valve on the manifold as I've described.

mboucher70 at wrote:          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.

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