RE: 5000S Air Conditioning System Problems

[Aleksander Mierzwa <alex@matrix.com.pl>]

I'm not an AC specialist nor have I BTDT, just thinking loud...
I guess enough pressure buildup could cause the compressor to stop
spinning and, in order, the clutch could burn. But such pressure would
probably blow a line first, and keep in mind that there's a safety
pressure switch that disengages the compressor in case of high pressure
in the system. A restriction in the circuit causing such enormous
pressure buildup would prevent the system from normal operation even if
the freon level was low. And you say the AC worked right after putting
the new compressor in. I doubt if the copressor cycling is a symptom of
low freon pressure. It is supposed to switch on and off to keep the
evaporator temperature at constant level. My compressor switches on and
off quite frequently, yet the AC works very good. I suggest that you let
a competent AC shop check and maybe partially disassemble the system to
look for a possible restriction (I doubt if it exists, though). A faulty
control unit could cause it only if both evaporator thermostat and high
pressure safety switch failed. To protect the new compressor I would
suggest that you adjust the compressor drivebelt a little loose. This
way the belt would rather slip than cause the clutch to fry.

Aleksander Mierzwa
Warsaw, Poland
mailto:alex@matrix.com.pl
87 Audi 5000CS turbo (mine)
88 Renault Medallion wagon (mom's)
91 mountain bike (just in case both cars broke at the same time :-)

> -----Original Message-----
> From:	Rossato [SMTP:rossato@erols.com]
> Sent:	Thursday, October 23, 1997 3:33 AM
> To:	quattro@coimbra.ans.net
> Subject:	5000S Air Conditioning System Problems
> [...]
> The A/C did not run.  I was told there was plenty of Freon, but the
> compressor was seized.  I had a junkyard compressor installed.  The
> shop
> was low on freon, but the compressor  was running.  I could see the
> clutch
> engaging and disengaging after a few seconds.  This would repeat after
> a
> minute or so.  I was advised that this behavior was related to low
> freon so
> I brought it to the shop to top off the refrigerant.  After adding a
> pound
> and a half of R12.  The compressor clutch burned out.  I was told the
> clutch was probably bad in the junkyard compressor.  
> [...]
> Further conversation led me to believe the clutch wasn't bad in the
> junkyard compressor, but that it burned once the pressure came up with
> the
> full Freon charge.  I was told that the clutches rarely fail on their
> own,
> being rather simple elecro-magnetic devices.  The casue of the problem
> is
> more likely a restriction in the system, I was told.
> 
> So, who has any suggestions?  I would gladly put in a compressor, if I
> knew
> it wasn't going to burn up the clutch immediately upon reinstalation.
> I
> believe I can replace the clutch, but the same logic applies.  Is a
> restriction likely to cause this problem?  If so, where?  How can I
> determine this?
> 
> BTW, the air distribution system is stuck on defrost and floor vent
> position, typical of a failed controller/vacuum system.  Could a
> failed
> controller be killing my compressor?
> 
> TIA
>