Climate control push button controller bad?
 

My climate control seems to work properly in Total Ventilation and defrost mode but not in the other two. In Normal and Economy the footweel vents do not open and the temperature wheel seems not to work. I can get full heat or no heat only in these modes out the defrost and side vents with cool air out the center vents. The car is a 1981 300TDt. Do you think I need a new push putton controller?

Oh boy! Welcome to climate control hell! Your symtoms sound more vacuum related. There are 5 switchover valves behind the pushbutton unit and some acuator "pods" that do the switching.
I'm also trying to work out a few problems so keep an eye on the posts!

Not before checking each vacuum actuator and the cabin temp sensor.

Sixto
91 300SE
87 300SDL
83 300SD

What are the procedures for checking the actuators and the temp sensor? Incidentally, I posted another question about finding the right page in the factory service manual. I have it on CD but can't find the right page. Service manual aside, though, are there quick and dirty methods for checking them?

You'll need the manual to find your way around the bowels of the dash. I don't know where to find the pertinent sections in the 123 CD manual but there should be a whole category dedicated to climate control.

To check the actuators, look for the ACC vacuum switching valve bank and test that each output circuit holds a vacuum. Note that one or more circuits might be tied in together so you'll have to test downstream of the switching valve bank. The manual will give you the spec but essentially you're looking for each actuator to hold at least 1/3 of a MightyVac gauge sweep for a few seconds. Maybe up to a minute or 30 seconds? I don't quite remember.

To check the cabin temp sensor, make sure that the hose to the aspirator motor is in place and intact (I don't know the layout of a 123), and check that the voltage or resistance is within spec per the manual for the ambient cabin temperature.

Sixto
91 300SE
87 300SDL
83 300SD

LOL - everybody that messes with these cars can relate to this:).
Pretty straight forward after you have learned all about Mighty Vacs, Klima relays and pressure switches. Just do a search:).

If you send me a PM with your email add I can forward a word doc that I put together thanks toa couple of members of this board that is a basic troubleshooting guide.

Your tools will be patience and a vacuum tester...