w126 heater vent intermitent by feet
 

My 1990 350 SDL does not consistently blow hot air from the vents in the footwell. It blows fine through defroster and dash vents but not at footwell. It seems to have no predictable pattern. Heater blows hot and all other controls work fine including AC. I've tried to search the forum so as to not waste anyones time if this issue has been reviewed priviously. Any help?
Thanks,
Adnre

300se
 

My 300se does the same thing......
It seems to mix the cool vent air and hot air??
Seems like the defroster is always on even with the A/C??
And help would be appreciated ...
-Anthony
1990 300se
1991 350sd
1972 280se 4.5
1967 250/280 se/c euro

Defrost is the default. You have most likely a leaky vacuum pod. The one that controls the flow to the footwell. I have the same problem and will be tackling it soon.

With the middle button in the PBCU pushed in, are you supposed to get hot air from the footwell as well as the two dash vents (leftmost and rightmost)? I've never had any hot air from in my footwells. How does one go about tackling this one?

The only time you are not supposed to get some flow from the footwell is in DEFROST and OFF.

I guess I have work to do then don't I? Anyone wish to tell me where to start? :)

There's a coiuple of places. First I'd remove the right side panel of the center console, to the right of the radio. There, you'll find a row of vacuum relays. The second one I believe is for the footwell. If you remove the vacuum line that is pointing toward the radio (it's the one going to the vacuum pod to control the footwell flap), you can put a mityvac on it and apply vacuum. The line should hold vacuum and you should hear the flap move. With the engine running and blower motor going, you should get air into the foot area. If you get nothing you can't hold vacuum, you have a leak.

Now it's time to trace the vacuum line to the diaphram. Wither it's a connection, or the diaphram is leaking. You can go here to buy a new rubber diaphram.

http://www.autoluxmbz.com/

1986 200SDL floor vacuum is #3, third line down.

Do you have no heat on floor at all, or just not driver's side?

I lost driver's side, see this thread.

http://www.peachparts.com/shopforum/diesel-discussion/109560-right-floor-heat-ok-left-floor-none.html

Loss of driver's side, but no passenger's, seems to be all too common, do a search, there are other threads.

Do a check for vacuum at #3. If you can remove the radio, you can see the vaccum pod and linkage, and confirm that it moves, or doesn't.

Let us know what you find.

Best Regards,
Jim

I get either heat on both passenger and driver side footwell or just hot air through vents. It will work fine for days and then will stop blowing in footwells. Sometimes I get into the car to drive home from work and it will blow at feet while it did not on the way to work. Sometimes it will just start to blow at feet while I'm driving after a while. It seems as the weather has gotten cold it works less correctly.
I have not taken anything apart yet.
Andre

OK, good show.

I'll second the suggestion by mplafleur that you remove the right side of console, unplug #3 vacuum line, put a tester (MityVac, etc.) and see if the operator holds vacuum. An intermittent vacuum leak in the dashpot or line could do what you're describing, and if too much vacuum leaks, the defrost vents will stay open in default. There is supposed to be a restrictor in this line, so an open line may allow some residual vacuum for the other actuators.

Of course, an intermittent electrical connection to the #3 vacuum switch could also be to blame, to put the vacuum gage on the #3 pipe on the manifold to make sure you're getting vacuum.

Hmm, if you have some extra vacuum line, a rubber fitting and a rubber "T" connector, you can leave the vacuum gage connected while you drive it. If you're lucky it will malfunction while you watch. At that point, you can see if you are losing vacuum faster than #3 pipe can supply it, or if the switch has closed. ;)

In any case, good hunting, and keep us posted, please.

Best Regards.
Jim