WHEEZING
air issue:
Contributed
by: Brian Smith
Webmaster
note: Brian Smith was nice enough to put together the below diagnostic
pertaining to 964/933 fan related problems. This is an on going WIP
as more information is discovered it will be posted on this page.
Normal operation:
- Recirc: Vacuum pressure pulls opens
inside air source / Servo Closes fresh air source
- Fresh: Vacuum releases & spring
loaded inside air source closes / Servo Opens fresh air source
The problem is that the electric servo
could die anywhere - fresh air source open, closed, or somewhere in between.
So the only real thing we are guaranteed to know is if the vacuum fails.
If vacuum fails, and servo still
operates:
- Fresh air selection: servo opens fresh
source, inside air source closed. NORMAL
- Recirc selection: servo closes fresh
source and inside air remains closed. NO AIR FLOW.
If vacuum works and servo fails with
fresh air closed:
- Fresh air selection: servo remains closed,
inside air closed. NO AIR FLOW.
- Recirc selection: servo closed, inside
air opens. NORMAL.
If vacuum works and servo fails with
fresh air open:
- Fresh air selection: servo remains open,
inside air closed. NORMAL.
- Recirc selection: servo remains open,
inside air opens. MAY APPEAR NORMAL, but can't shut off outside air.
So to sum up:
- No air flow/Wheeze on recirc - you
have a vacuum leak somewhere:
- No air flow/Wheeze on fresh - your
fresh air electric servo has died in the closed position.
To verify electric servo:
- Remove black plastic trim under front
hood nearest to the base of windshield and locate center electric servo.
(There are 3 servos on a 993, one to open/close footwell output, one to
open close windshield output, one to open close fresh air input.) 964's
have 2 more to control temp mixers. 993 temp mixer servos are in cabin
under door sill trim area.
- Operating the corresponding a/c control
should show servos moving back and forth.
To verify vacuum -
- Main vacuum "source" from engine routes
to same location as the 3 servos, into an electric solenoid. When the recirc
button is pressed, the electric solenoid opens the valve, passing vacuum
pressure to output. With engine idling:
- Disconnect vacuum source on solenoid
to verify vacuum pressure. If not present, problem is vacuum leak in engine
area. (Good luck)
- If vacuum present, press recirc, disconnect
output side of solenoid and verify vacuum pressure.
- If not, solenoid not getting signal
or failed.
- If present, look under dash, under ccu
for rubber elbow connecting vacuum line to flap mechanism - it would most
likely be unplugged due to stereo installer or other inside work bumping
it free.
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