Re: 90q A/C compressor hose leaks

["Fred Munro" <munrof@isys.ca>]

-----Original Message-----
From: Andrei Kogan <abk@phy.duke.edu>
To: quattro@coimbra.ans.net <quattro@coimbra.ans.net>
Date: Wednesday, October 21, 1998 3:19 PM
Subject: 90q A/C compressor hose leaks


1. The guy who looked at it got me confused. he told me, it was the hose
>that goes to the condenser, and it was on the low pressure side of the
>compressor. Isn't the condenser located on the high pressure side? My
>understanding of the the AC cooling is that the compressor lowers the
>pressure in the evaporator which causes  the liquid agent to
>evaporate/absorb heat, then compresses the hell out of the vapors  which
>causes them  to condense and release heat some place else. At least this is
>how the helium-4 cryostat operates in my lab :-)
>
>2. Just realised that there could be a different cooling principle used
>--Joule-Thompson effect. In this case, the cooling would  be generated by
>forcing the agent through a flow restriction rather than by evaporating the
>liquid. It would still mean that the "condenser" , that is, the place were
>the heat is released, is on the high pressure side.  Could someone tell me
>which design is used, or is there some other principle involved that I am
>not aware of?

    You've got it! A restriction in the high pressure line causes the liquid
to expand into a cool gas. The expanded gas enters the evaporator which
transfers heat from the air entering the car to the cool gas. The now hot
low pressure gas enters the condenser (mounted in front of the radiator)
where it is cooled. It then enters the low pressure side of the compressor,
is compressed to liquid, and the cycle repeats itself.

>3. Are the compressor  hoses hard to replace? If they aren't too expensive,
>I would probably just do both of them. What should I watch out for --- any
>tricks when attaching them, or dealing with the a/c system in general. Is
>there a diy procedure for checking if the system is OK for recharging?


    Andrei, it is an offence in most jurisductions (as well as
environmentally unfriendly) to vent A/C coolant to atmosphere, so unless you
have a coolant recovery system or have your coolant removed at a shop, it is
"illegal" to do your own work. That said, here are some pointers.
    Moisture is the enemy of A/C systems. When replacing the hoses, keep the
time the system is open to atmosphere as short as possible. The system is
charged with a fixed amount of lubricant, so any removed in components must
be replaced with the same amount removed. After assembly, pull a hard vacuum
(24 inches Hg) on the system for several hours to boil off and remove any
moisture. Leave the vacuum in the system for an hour or so and retest - loss
of vacuum indicates a leak. The system must completely evacuated before
charging.
    Some techs recommend changing the drier whenever you open a system up,
but I never found it necessary - depends on the system.
    I have never replaced my hoses, but other listers have mentioned that
they are very expensive. Some have had hoses made up at A/C shops.

HTH

Fred Munro
'91 200q  261k km