Matt this is a great question!  First of all let me say that VW Diesel
Vanagons do not have Air Conditioning.  Actually there is a warning
sticker on the stock cover for the timing belt that says something to
the effect of "Warning do not install A/C on this van!!"  So my reply
will come from the diesel Jettas that I have worked on over the years.
To my knowledge the 48-93 VWs (gas or diesel) A/C system was pretty
simple.  It does not look at engine rpms at all.  Some of the very early
primitive versions came on no matter what unless the thermostat told
them to go off.  The newer ones (84-93) have high and low pressure
sensors in the A/C system.  These turn the compressor off (disengage the
clutch) when the refrigerant pressure is either too high or too low.
Kinda stinks when you are trying to charge an empty system because the
stuff sometimes doesn't want to bring the low pressure switch on (not
enough pressure).  Some folks actually hot wire the compressor to allow
it to suck in enough refrigerant to get things started.  So now you know
and knowing is half the battle!!!

Thanks,
Ken Wilford
John 3:16
http://www.vanagain.com
http://www.strictlyvwauctions.com
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Phone: (856)-327-4936
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-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
Of Matthew
Sent: Thursday, April 29, 2004 5:12 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Diesel AC question. WHat triggers the clutch?

I am helping a friend convert a gas-powered land
crusing to a diesel powered land crusier. check out
this link for his details, insane what he has done:
http://forum.ih8mud.com/index.php?board=21;action=display;threadid=13204

Anyways, the old (gas engine) ac system has a switch
that is triggered by a pulse coming off the
distributor, so it knows at what rpms to shut off the
AC compressor. Diesels don't have a distributor...

So, on vw diesel engines, what controls the compressor
clutch? Is there an automatic switch that will turn on
and off the magnetic ac compressor clutch when the
engine rpms are too low? How does the vw diesel setup
work for ac?

thanks
matthew

=====
Matthew Pollard         "Racing with the wind and flirting with death
Dept. Of Chemistry     So have a cup of coffee and catch your breath"
University of Idaho
www.ftir.chem.uidaho.edu

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