w124 heat or a/c always to dash vents
 

Hello,

I have an 86 300e that I bought about a year ago. The heat or a/c always blows to the dash vents when the system is on. Is this a common problem? I have not seen this symptom mentioned in the searches I have done.

To describe it further, when the push buttons are in any position but 0 (off) I get heat or a/c depending on where the temperature wheel is set, including cooling when in EC (economy?) mode. No air to the floor or defrost as the arrows on the pushbuttons promise.

Is this a symptom of vacuum pod failure or perhaps a failure mode of the control unit? Thank you for your advice!

Tom
Austin, TX
86 300e 5spd

vacuum leak somewhere.

If I remember right, the 'default' flow is NOT is not out the front vents. I think the default position of the defrost pod is open, not closed.

Not too hard to check your pods - probably at least some are bad. Check them and then at least you will know. If you have no defrost flow, I think the defrost pod must be good. If I remember right!

I did have a bad manifold once - the part with all the vacuum hoses on it, behind the glove box. I had a bad control unit once, also.

Most likely a bad pod. To confirm this, remove the glove box liner and use an auxiliary vacuum source on each of the vacuum lines as they are removed one at a time from the vertical maniold at the left bottom of the glove box opening.

If you have a bad one, which is highly likely, replace them all. It is a BIG job to remove the dash to replace them so, do them all while you have it apart. This is about a fifteen hour job, maybe not quite that long, but it won't miss it by much.

This is correct. In the 124, no vacuum will default the defrost to open, and the center dash vents to closed. To see if you have an improperly hooked-up vac-control unit try un-plugging the vacuum source under the hood and it should default to defrost.

Thanks for your advice! I will start with the vacuum check under the hood, then behind the glove box.

Tom