Backwards Air Recirculation Fixed!

["Dick Green" <dick.green@valley.net>]

Well, I got only one response about my problem. The advice was OK, but I had
already tried it. I finally decided to take nut driver and screw driver in
hand and fix the darned thing myself.

The problem and solution turned out to be very simple. In fact no
disassembly would have been required to fix it, but since I didn't know that
at first, I had to remove the glove box and ventilation fan in order to
figure out how everything works and locate the problem.

The ventilation system is supposed to default to sucking in cold air from
the outside through the windshield vents. When you hit the recirculate
button, a small flap, about 4" x 6", flips up to cover the outside opening
and expose an opening into the passenger compartment under the glove box.
The flap is moved by a gear and arm assembly. The arm is vacuum actuated via
a small vacuum switch behind the glove box. Pushing the recirculate button
applies +12VDC to the vacuum switch, which connects the vacuum pump to the
actuator, which pulls in the arm to open the flap. When the recirculate
button is pushed again, the switch closes, vacuum is removed from the
actuator, and the arm extends to close the flap.

In my case, as soon as the car was started, the flap would open into the
recirculate position. Pushing the recirculate button caused the flap to
close into the fresh air position. Obviously, this was backwards. It
explains why the windows were fogging up in cold weather (when the A/C was
off) and why I kept hearing a rushing noise.

At first I thought that either the flap or actuator assembly had been
reassembled backwards by the dealer when they replaced the A/C condenser.
But that did not appear to be possible. Given that the door was opening when
the car started, it seemed that +12VDC was being applied at startup and
maybe the voltage feed was somehow reversed. But that made no sense at all
(unless the computer was mighty confused), and this was confirmed when I
measured the vacuum switch voltage at startup and found it to be only a
couple of hundred millivolts  -- not enough to activate the switch. I
wondered if maybe it was a latching switch or something and I just wasn't
seeing the pulse. But it still made no sense to me that the default would be
for the switch to be activated all the time.

Finally I removed the vacuum switch and examined it. While you would think
that the switch would simply have one vacuum input port and one vacuum
output port, it in fact has three ports! That immediately raised the
possibility that the input and output hoses might be connected incorrectly.
By applying +12VDC to the switch and blowing through all three ports I
quickly found the correct arrangement. There is one input port and two
output ports. Just like an electrical relay, one output is NO (normally
open) and the other is NC (normally closed). Applying voltage closes the
open port and opens the closed port. Obviously, the hoses had been connected
incorrectly -- the input hose was on the NO port instead of the NC port, so
the vacuum was always passed through to the actuator unless the
recirculation switch was turned on. That explains why the flap opened as
soon as the car started and the vacuum pump got underway. The output hose
was connected correctly. All I had to do was move the input hose to the
input port and the flap started acting exactly as it is supposed to act.

Problem solved. I could have done this by simply reaching under the glove
box to move the input hose. In fact, the vacuum switch could have been
removed that way, too. Removing the glove box and fan (the latter was not
completely simple) was unnecessary. Oh well.

Guess the dealer's mechanic screwed up the A/C condenser replacement, eh?
Well, maybe not. After I got the car back last year, I had to fix up the
cables going to my dash-mounted cell phone and ham radio. The dealer had
messed those up and had broken a connector. I have a vague recollection of
reconnecting that input hose, which is in the same area as the cables.
Perhaps I accidentally pulled it out and reconnected it to the wrong port
myself. Or maybe the dealer forgot to reconnect it and I found it dangling
there. Or maybe they really did connect it wrong...

In any event, it's amazing that I've been driving around for a year with no
fresh air in the passenger compartment!

Dick Green