W126 recirculation flap test - PeachParts Mercedes-Benz Forum

Usaguy · #1 04-03-2021, 06:13 PM

Anyone knows an easy way to test if the recirculation flap closes on a 126?

I have a feeling that mine stopped working.

For those of you unfamiliar with this system the recirculation flap is supposed to close 80% in the "O" and the A/C buttons (all 3 buttons from the left) but is supposed to be open only in the EC position.

Anyway here are my symptoms:

How it used to work: switching from EC to O: I can hear a slight thump and I get no ram air.

How it works now: switching from EC to O: No thump and I get ram air (which is not supposed to happen)

The reason why I want to check this flap is because it will impact the performance and reliability of my A/C system in the coming summer months

Diseasel300 · #2 04-03-2021, 08:40 PM

Assuming this is your 1990, pull out the glovebox liner or passenger airbag, whichever is fitted. You should be able to observe the flap operating in the rear part of the dash through the hole. Turn the A/C temp wheel all the way cold and hit the recirculation switch on the dash, you should see it fully close the outside air portion of the flap (100% cabin air).

Be aware that there is a switchover valve block around the knee area in the center console on the passenger side. The solder breaks internally where the individual solenoids are mounted to the printed circuit board. Cut the back off with a hot knife and resolder everything inside. I've redone close to a dozen of them and every single one had broken joints. It's also very common for the rubber elbows that connect the vacuum lines to said switchover valve block to split and leak vacuum.

Usaguy · #3 04-03-2021, 09:03 PM

Quote:

Originally Posted by Diseasel300

Assuming this is your 1990, pull out the glovebox liner or passenger airbag, whichever is fitted. You should be able to observe the flap operating in the rear part of the dash through the hole. Turn the A/C temp wheel all the way cold and hit the recirculation switch on the dash, you should see it fully close the outside air portion of the flap (100% cabin air).

Be aware that there is a switchover valve block around the knee area in the center console on the passenger side. The solder breaks internally where the individual solenoids are mounted to the printed circuit board. Cut the back off with a hot knife and resolder everything inside. I've redone close to a dozen of them and every single one had broken joints. It's also very common for the rubber elbows that connect the vacuum lines to said switchover valve block to split and leak vacuum.

Yes it's the 1990 and I do have a passenger airbag.

I was thinking of somehow sticking a remote camera in there but may have to resort to removing the airbag.

Yes my first suspicion was the switchover valve but I will do some more diagnosing before pulling and re-soldering it.