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RE: Where *is* the low pressure AC port?

Thanks, Scott & Igor. I have filed your excellent response in my AC folder.
I actually had a can of R12 that I bought about 15 years ago at a going out
of business sale for a buck. I bought a pressure testing gauge at my local
Pep Boys, along with the little tool that pierces the can and routs the
Freon to the fitting via a rubber hose. When I measure the pressure on the
low side at 1500 rpm after equilibrating the system, I found that the system
was low on R12, so I added my precious can via the low pressure port located
on the compressor. After adding the can, the system was in the normal range
for pressure. The system was working reasonably well before, but making a
howl, especially at low speeds. The howl is much reduced, so, I assume that
the lubricant (according to the can, it had R12 lubricant as well as a leak
tracer dye included) has helped the howling problem. The AC works just fine
now. Thanks for you help.

BTW, the little gauge that I used also allows you to test on the high side,
where I again found the system to be within expected pressure levels. I used
the hi-side port in front of the radiator. It was much easier than I

Paul Meyers 87 5KCStq 130K mi 5spd, Silver. Stock + Fuch wheels

-----Original Message-----
From:	Scott Mockry [mailto:scottmo@teleport.com]
Sent:	Monday, July 05, 1999 12:19 PM
To:	Igor Kessel; paulm@viewsoft.com
Cc:	quattro@www.audifans.com
Subject:	Re: Where *is* the low pressure AC port?

At 01:43 PM 7/5/99 -0400, Igor Kessel wrote:
>On my both type-44 ('85 5000s and '89 200TQ) and on the one that used to
>belong to my friend ('87 5000s) the low pressure port was the low
>pressure switch under the cowl. The A/C compressors in all three were
>Nippon Denso.
>Recently Scott Mockry posted that his '89 200TQ had a Sanyo compressor
>and the low pressure port was where you are describing.

Igor and Paul,

My reference to a "Sanyo" compressor was incorrect, having a bad Asian

All the compressors I referred to are Nippon Denso (ND) units. I have two
1989 200TQ's in my driveway at the moment, (one sedan, one wagon) and they
both have ND units installed which have a low pressure port on the
compressor (located on the manifold that bolts on the compressor). I also
have two compressors laying around,  one from a 1987 5000TQ and one from a
1987 5000T and they also are ND compressors with the low pressure port on
the compressor. The only difference I could see between the 1987 and 1989
ND compressors, was the 1989 unit has a high pressure relieve valve
installed on the compressor manifold (high side).

Using the fitting for the low pressure switch which is located under the
plastic cowling near the windshield would also work fine. You just need to
pull up the plastic cover and unscrew the low pressure switch. In some
cases, you need to jumper across the low pressure switch after initially
adding freon to keep the compressor clutch engaged during the recharge

The main thing to keep in mind, is you don't want to try to add freon to
the high pressure side when the engine is running and the compressor clutch
is engaged and turning.

If you decide to do any A/C work which requires removing a compressor or
lines, and the system is still charged with freon R-12, you may want to
visit a shop with a recycling A/C unit, and have them suck out the
remaining freon as this stuff is expensive ($20-35/lb) and reportedly is
harmful to the environment. Make sure the replacement compressor or
component has the appropriate amount of refrigerant oil inside before

You also want to make sure the system is sucked down for about 30 minutes
with an appropriate vacuum pump, to boil off any moisture in the system
before recharging.

Replacing the receiver/dryer assembly is also a good idea if you are
replacing a compressor or have had an open/leaky system for awhile. There
normally is a desiccants packet inside the receiver/dryer to absorb
moisture and they can get saturated over time.

Scott (Not-Sanyo) Mockry