My heating system has been on the blink for a year. Fan sometimes works sometimes doesn't (replaced the brushes so its not that), no temp control (only on or off), no heat unless the unit is turned on when you start the car, if heater working and you turn off the heat then it won't come on again.

Anyway...fixed it!

Took out the climate control unit and removed the liitle board at the side of the temp wheel...snaps out but watch for the spring, ball bearing and little copper contact. The copper contact and the inside of the board were very dirty and covered in a dustry crud...kind of like the lint that will gather on the rollers of your mouse. Cleaned up both the board and the copper contacts with alcohol, put back together and reinstalled and now the heater works fine.

While apart I also made sure that the heater hose/channels were air tight. The ones to the heater box in the central console needed some extra weather stripping to seal them and so did the hose going up.

Now all functions are back to normal. Amazing! I guess these things are only as good as their weakest link.

While apart though I noticed that the large flap behind the glove box closes very slowly. Used to be I could hear those flaps shutting and opening with a "snap" (especially when pushing the defrost button) but not anymore. Anyone have any ideas on that?? Still works but slooooowly.

Spoke too soon..!

I'm still not getting adequate airflow. With the ducting under the glove compartment removed there's a good blast of air coming out of the central console but when that ducting is replaced its hardly noticable.

Any ideas???

That slow flap problem would most likely be vacuum related as the soleniods that power these are all vacuum controlled. My guess is that the problem with airflow is the same issue.
If one "door" is not opening fully it might cause the outside air to not get through to the heater box hence no airflow in the heater mode.
It took me about three days to actually figure out what all the vent doors opening and closing in combination did inside my old 115 but once I figured that out and then fixed the vacuum leaks it worked great.

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

Vacuum leak for sure. Either the supply hoses are bad (check all the rubber connectors, they are usually dead by now and leaking) or the servos themselves are going. Won't move at all when shot.

Get a MitiVac hand pump, it will be invaluable in chasing down the leaks. I ought to see if I can the the manufacturer to pay me, I recommend them nearly every day on the forum!

Hook up the pump and see if the system as a whole holds vac (the green plastic line by the brake booster). If it does, then the leak is in the engine compartment or the line is plugged, or the vac pump is sick. If it leaks down, the leak(s) are in the climate control and you will have to chase them down.

Good point about the electrical contact, though -- both my W124's have wide temp variations and the 300D runs cold sometimes -- may need to do your repair to mine after I check the sensor hose.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!