stuck on defrost in my w123 wagon
 

My 300TD is stuck on defrost setting. No matter what I do I can't seem to get the front climate controls to not be on defrost. help

the engine shuts off & the brakes work fine so its not a vacuum issue. seems like its a climate controller button not "popping out" when changing modes...

I'm going on memory so I may or may not be right. I seem to remember that defrost is the default mode when the pushbutton unit quits working.

I’m pretty sure defrost is the default mode when the CCU looses vacuum supply. Green with yellow stripe IIRC

it is the default by my indie, but i checked vacuum and it's there...

Take the CCU out of the dash, and twist it and squeeze it while the engine is running. CCU issues are often bad connections on the circuit board and twice i have diagnosed a bad CCU by having it work correctly while holding it and twisting it gently.

wheres the ccu on a w123?
thx!

It is the pushbutton unit.

thx

Turns out I have a spare unit in my garage. :) I'll swap it tomorrow.

There you go.

Right. ^^^

Replace that row of selector buttons. I had to do that on my '83 300SD - problem solved... It was a pricey item, as I recall at the MB Dealer.

So my spare 123 830 12 85 unit operates only when twisting ...
However the 107 830 26 85 which was rebuilt and is the exact same size + takes the saw fittings functions perfect.
Why shouldn't I use the 107 unit?

Thx srj!

If anyone needs a PCU rebuild check out ProgRama.