W126 Climate control
 

On my '82 300SD I am having erratic operation of the climate control. I am sure that all the vacuum doors are operating, the problem is that often I get no heat/air out the floor vents just out the defroster. If I switch unit off and push the slow speed fan button and then switch back on to economy everything seems fine and will run that way till I push one of the other buttons and then I just get defrost air. IS the the push button control that is fritzing or is it something else? HELP!:(

Just to add to my previous post. For no reason it went on to full defrost out of the blue with the EC button pushed. I pushed the low speed fan button and the fan did as commanded but it still put all the air out the defrost. Another time I rolled the temp wheel to min. and then back to 22* and it did it's defrost trick. Is the culprit the climate control module(push buttons)?

You might have to replace the climate control. They are notorious for going out. If you can. You open up the board and see if the solder is broken in the climate control but, do a search on it. There is a lot of info on this.

S60

You are referring to the pushbutton unit? Just want to clarify that we are talking about the same unit. I agree that the way it is acting that it must be the control unit. Does not seem to have symtoms of a vacuum/solenoid problem, to erratic for something mechanical.

I suppose it could be a faulty climate contril unit, but for alot less $$, I'd look at the monovalve insert. I'm assuming your yr. model has such a device(monovalve). Check out the search facility here for "monovalve". This device or should I say, a faulty monovalve insert diagraphm is notorious for flaky heater operation.

Worked perfect today. Go figure. Acts like electronics. Temp control works fine so I am confidant that the monovalve is fine. Will a broken soldered joint cause a problem like this or is more likely an electronic component failing?

I WOULDN'T DISMISS THE MONOVALVE. I WENT THRU A FLAKY HEAT SCENARIO LAST WINTER(126 CAR) AND IT TURNED OUT TO BE THE MONOVALVE DIAPHRAGM INSERT($20 PART).

NOT SAYING THIS IS YOUR PROBLEM - JUST SOMETHING TO THINK ABOUT.

Bribenz - guess I'll take a reading course over the holidays - I reviewed the orig. post & you are correct. It's not a lack of heat.