I've scanned the archives and didn't spot the answer to my simple question. So --- how are the flaps (openings) for different heat / defrost modes opened and closed. I know they are vacuum controlled, but are they actuated mechanically by the CCU buttons, acutated electrically by controls from the CCU buttons, or just what? My 300D just developed electrical problems (fan won't come on) on the same day that it also developed vacuum problems (transmission actuator, I think). I think the timing is merely coincidental, but a little advice would be welcome.

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John Schroader
bio burnin' 83 300D, '83 300 SD, '79 240D
"I've never met a man who was good at making excuses who was good at anything else" Ben Franklin
"You cannot permanently help a man by doing for him what he could and should do for himself" Abraham Lincoln

On the 123's, mechanical. Fan problem possibly CCU failure, fairly common. Vac could be any number of things. Tranny only?

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83 SD

84 CD

First mention the car or put it in the signature.

The flaps in a 1983 W123 300D are controlled thru various things. Your buttons control the amp which controls the air switches behind the AC control panel. And the air switches route vacuum to control the elements that control the flaps.
So your flaps are controlled by elements. And the elements are vacuum actuated and electrically controlled.

So your problem.
Check the fuses. Al of them and check for corrosion on the fuse contacts.
Try going to full fan speed by pushing the top fan button. If nothing then remove the fan and place 12 volts on it to check it.
Transmission, Sounds like a vacuum leak somewhere. It could be the control valve on the injection pump but first check all vacuum connections hoses and the vacuum pump output. You do have aMityvac or equivilent?? Poor vacuum means harder shifts.

Go in the engine compartment with some golf tee's. Just to the left of the brake booster is are the vacuum lines going into the cabin. Disconnect the following lines one at a time, block and then see if the tranny shifts better.
Yellow based lines, 2. For the door locks.
Green based lines for the AC system.
Brown lines are for the engine shutoff.
See if anything changes in the operation.
This will look at vacuum problems.

If the problem is the AC unit. Which does give problems, the solder joints crack and must be re soldered. We will figure this out later.

So check the fan with the buttons and the direct voltage.
Check the vacuum system for a leak as I posted above and lets see what that gives us.

Dave

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car

Many thanks fellows. As for the vacuum leak - - the transmission has shifted hard since I bought the car (3K miles ago) but recently the engine would not shut off. Bought a mightyvac and tracked the leak to the transmission. Ordered a new modulator today. As for the blower, the fan works fine when connected to an independent 12v source. Took the control unit out and cleaned the connections (not inside unit, just pins on both sides). Worked two times and quit again. I'm pretty good at electrical circuits but vacuum is a new game. Just wasn't sure what made those flaps open and close. Gonna pull the control unit out this weekend and tidy up the internal connections. Again, this forum is a lifesaver.

__________________
John Schroader
bio burnin' 83 300D, '83 300 SD, '79 240D
"I've never met a man who was good at making excuses who was good at anything else" Ben Franklin
"You cannot permanently help a man by doing for him what he could and should do for himself" Abraham Lincoln

Keep us posted.

__________________
83 SD

84 CD

Got the modulator in the mail yesterday. Printed out all the info I could find. Will install soon. Any words of warning? I'm tired of learning the hard way.

__________________
John Schroader
bio burnin' 83 300D, '83 300 SD, '79 240D
"I've never met a man who was good at making excuses who was good at anything else" Ben Franklin
"You cannot permanently help a man by doing for him what he could and should do for himself" Abraham Lincoln

Find Steve Brotherton's article about adjusting that modulator...
he is a moderator on this site but another forum....the definitive information on that deal...

Those symptoms suggest that the problem is cracked solder joints in the CCU. Reflow the joints where the vertical terminal boards meet the horizontal circuit boards.

In reference to the flaps, they vacuum operated, but the vacuum is electrically switched.

Also re-solder the relays while you have it apart.