Kneale Brownson kneale at coslink.net
Mon Dec 19 05:48:36 EST 2005

Recirculation flap failure usually leads to fogging of ALL windows in the
car.  If all you have is the rear window fogging until you turn on the
defogger, I think you have "normal" performance for your 1980s Audi in cold
weather with a load of passengers.

Again, the recirculation flap should be closed during heater operation so
that warm, moist air from the cabin isn't added to the air passing over the
heater core to create even more moist air coming from the vents.  You can
check it by putting your head in the passenger footwell and looking upward
past the back of the glove box with a flashlight.  If you see an open door
with a spring hanging from it, you have either the common broken spring
perch in the evaporator box or the broken end of the spring.  If you see an
open door with no spring visible, you have lost the spring due to either of
the previous problems.

At 10:19 PM 12/18/2005 -0500, Max Hoepli wrote:
>I don't think so, no dripping inside the car, no pooling.
>Have had following answer which is most probable cause:
>One of the most common causes of cold weather interior fogging in the 5000
>series cars is failure of the recirculation flap spring. This allows the
>recirc flap to open and recirculation moist interior air. No dry outside air
>is drawn in through the H/V system. The recirc flap is located inside the
>car under the passenger side dash on the A/C evaporator box. The spring
>mount usually breaks off the flap, allowing it to open.
>The vents you are referring to allow the outside air pulled in by the H/V
>system to exit the car. If they are not open, you wouldn't have any air
>flow, but I've never heard of these vents failing. I have heard of lots of
>recirc flap failures though.

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