More AC - 90 CQ

Ameer Antar antar at
Tue Jul 1 14:38:45 PDT 2008

Sounds like it could be a high pressure switch or blockage of the expansion
valve. I would check the high/low pressure switches and wiring. Then some
pressure checks are in order. If there is some partial blockage in the
system, too much pressure will build up and then the switch will disengage
the clutch. The pressure goes down, the system resets and then cycles over
and over. The blockage is usually in the expansion valve as there is a
screen in there to protect the valve.


Message: 7
> Date: Tue, 1 Jul 2008 09:37:58 -0700
> From: Max Baker <max at>
> Subject: More AC - 90 CQ
> To: quattro at
> Message-ID: <20080701163758.GA21717 at>
> Content-Type: text/plain; charset=us-ascii
> Hi List,
> As long as we're on AC problems here, I've got a 1990 CQ with the AC
> Delco-style automatic climate controls.
> The problem I'm having is that the AC cycles on and off at about a 45
> second period.  I set the controls to auto/LO/fan high and rev'd the
> motor.   I can see the clutch on the AC compressor coming on and off at
> the 45-second interval.  It's very annoying while driving because the car
> lurches a little every time the compressor comes back.
> I'm hoping it's just low on coolant and I can find some R12, but does
> anyone have any other ideas?   I still haven't found a Bentley for this
> car, so I don't have the factory service checklist for this AC system.
> Thanks!
> -m
> ------------------------------

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