1980 300d "off" pushbuttons not working
 

I have finally gotten my a/c situation in order. But, pushbuttons in the "off" position does not go off. It continues to blow on low setting. All other buttons work fine. Heating and cooling work fine. I have vertical buttons. Any idea what could remedy this problem. I can buy the new pushbuttons for $140 at Dealer. Just not sure this will fix it. Not returnable.

The other thing is that when I start the car the a/c will not go on without giving a little throttle. Push the footfeed and a/c then goes on. Wierd. I guess vacuum increases enough to activate the system.

Paul

Yes sounds like you still have vacuum issues run through the system again.

Vacuum
 

When I mityvac the green line at engine I can not hold vac at all.
Is this right.
WHat vacuum # should I be getting at the green line?

I tried another 300d car and got same results. Other car works fine. a/c wise.

No matter how much vacuum I apply to the (green) climate control line on engine side I can't get the "off" button to turn system off. Thats what confusing me.

I plugged ignition and door lock lines to pull only on climate line with mityvac.

Not the same CCU, but my 124 did the same thing, fan would run in OFF position, replaced CCU and all was solved. Replaced seized aux. pump also (after CCU replacement solved the fan issue).

Vacuum only determines which vents are open. It has nothing to do with the A/C clutch engaging or the blower control.

Sounds like you have a bad pushbutton unit for the off problem.
As for the A/C compressor clutch not engaging, I'm not entirely familiar with the klima relay, but I'm pretty sure if won't engage until the engine gets above a certain temperature or something like that, the idea being to keep the engine from trying to turn the compressor and stalling out.

all the off button does is disengage the other buttons. it's purely mechanical. you may be able to dissassemble it and repair the problem, but a new unit may be needed.

Heh, incidentally, my off and defrost buttons don't disengage whatever is pressed, so I can't turn off my ACC either. At some point I will probably take out the pushbutton unit to test it.