Checking For Leaks on Fresh Air/Recirculated Air Flap

Checking For Leaks on Fresh Air/Recirculated Air Flap








Check valve (31)
Check for leaks, section a.

Tests b to d
Prepare.

Vacuum circuit 1, fresh/recirculated air switch (S24) and air volume switch (S3)
Check for leaks, section b, at blower stage 1 and with fresh/recirculated air switch off.

Vacuum circuit 2, vacuum elements for fresh air/recirculated air flap (33), long stroke
Check for leaks, section c, at blower stage 1 and with fresh/recirculated air switch on.

Vacuum circuit 3, vacuum element for fresh air/recirculated air flap (33) long and short strokes
Check for leaks, section d, at blower stage 0.


Permissible leakage
Permissible leakage per vacuum circuit 30 mbar/min at 400 mbar vacuum
(without vacuum supply tank)

Permissible leakage of check valve 50 mbar in 10 min at 300 mbar vacuum

Permissible leakage of other components 20 mbar/min at 300 mbar vacuum







Special tool


Self-made tool
1 blind plug 000 987 11 45


a) Checking check valve (31) for leaks







1 Disconnect dark red. green vacuum line and green red vacuum line from check valve (31).
2 Connect tester (arrow) to check valve. Seal off second connection with blind plug.
3 Evacuate with tester and read pressure gauge. If the indicated pressure rises, renew check valve.


Preparing tests b to d







1 Disconnect green/red vacuum line from check valve (31) and connect tester to this vacuum line.
2 Switch on ignition.


NOTE: The tester remains connected to the green/red vacuum line for the entire duration of the test.


b) Checking vacuum circuit 1, fresh/recirculated air switch (S24) and air volume switch (S3) for leaks
1 Move air volume switch to stage 1.
2 Evacuate with tester (approx. 400 mbar) and read pressure gauge.
3 If the indicated pressure changes, check the fresh/recirculated air switch (S24), the inner connection of air volume switch (S3) and the vacuum lines, and renew if necessary.




Vacuum circuit 1, air volume switch at stage 1 and fresh/recirculated air switch off
S3 Air volume switch
S24 Fresh/recirculated air switch
33 Vacuum element for fresh air/recirculated air flap


c) Checking vacuum circuit 2, vacuum elements for fresh air/recirculated air flap (33, long stroke) for leaks
1 Switch on fresh/recirculated air switch.
2 Evacuate with tester (approx. 400 mbar) and read pressure gauge.
3 If the indicated pressure changes, check vacuum elements (33) and renew if necessary Service and Repair, or check green vacuum line and renew if necessary.




Vacuum circuit 2, air volume switch at stage 1 and fresh/recirculated air switch on
33 Vacuum element for fresh/air recirculated air flap


d) Checking vacuum circuit 3, vacuum elements for fresh air/recirculated air flap (33, long and short strokes) for leaks
1 Move air volume switch to "0"
2 Evacuate with tester (approx. 400 mbar) and read pressure gauge.
3 If the indicated pressure changes, check vacuum elements (33) and renew if necessary Service and Repair, or check green/blue vacuum line and renew if necessary.




Vacuum circuit 3, air volume switch at "0"
33 Vacuum element for fresh/recirculated air flap