Air vent door won't close

[Huw Powell]

> '87 4000 Q air vent door does not close when air conditioner is turned on.

I presume you mean the flap that blocks the fresh air intake to the 
white plenum under the hood, making it so air is drawn over the AC 
evaporator.

There is an electrical switch on the heater control (I can't remember if 
it is the "AC on/off" switch or one built onto the temp control slider) 
that actuates a solenoid next to the plenum.  This vacuum solenoid 
operates a servo on the side of the plenum which closes the flap.

(earlier style type 85/81 cars have a vacuum switch right on the temp 
control slider)

So, first, fire the car up and set it so the flap should actuate.  Then 
check voltage at the solenoid, vacuum supply to the solenoid, correct 
function of solenoid.  Check the servo and flap providing your own 
suction, and of course the condition of the various vacuum hoses.

The vacuum "comes from" the intake manifold via a one way valve, and a 
bit is stored off a Tee fitting in a plastic reservoir under the fender.

This might be the same vacuum storage used for the diff lock actuation, 
not sure about that, though.

Good luck!

-- 
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/