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Subject: air con.

Dave (and Chewy) wrote:
Okay, time to call upon the collective knowledge of the Qlist.  Having
problems with getting the compressor to engage on 89 200tq.  Known: 1) Have
power to low pressure switch.  2) Able to engage compressor by jumping wires
at compressor.  What we are having a problem with is the fact that we cannot
get voltage or find the wire for that matter that flows from the low pressure
switch over to ?  Is there a relay somplace for this?  Fuse box
has a listing for (2) two relays but there has never been a relay in that
location for as long as I remember. (Air used to work very well)
The air conditioning/climate control unit (CC) in the 100/200 '89-91 cars uses
two exterior temperature sensors, two interior temperature sensors, engine
coolant temperature sensors, and has input for the ECU to turn off the
compressor under high load, or high heat conditions.  Overall, a highly
integrated unit, pretty sophisticated to blindly troubleshoot.  The CC opens
and closes the coolant valve to the heater core, controls the recirculate
flaps, controls which vents get air when, controls fan control speeds, and
controls the flow of air across the heater core, and advances the idle when
the compressor is engaged.

The bentley manual has an extensive troubleshooting procedure in it using the
CC head unit to generate codes.  The codes tell you the values recieved from
the various temperature sensors, the positions of the various control flaps,
and known errors.  

There's a writeup on this procedure on the 20-valve pages at:


This is from the Bentley manual for the coupe; the setup is similar but not
identical.  As many people can tell you, the system can be somewhat
frustrating to put right, even when you know what you're doing.  However, I
feel it does a very good job when functioning.

Best bet is to buy/borrow a bentley manual and run through the procedures.  I
have one and can assist if you'd like.  Manuals can be purchased from various
booksellers, etc.  I've got a description of the book, and a link to
Amazon.com for purchase.  I think retail is about $180; discount via mail is
around $120 or so.
HTH, Chris Miller, Windham NH, c1j1miller@aol.com
'91 200q