300SDL...A/C works. heater doesn't
 

Well, it's finally fall here in Phoenix. I went to test out the heater the other day (so I could keep the sunroof open, of course) :) It didn't heat up at all, even with the temp set to 28C or whatever the highest reading is. Is there a solenoid valve that allows coolant to flow through the heater core? Where would I find this piece. Unfortunately, the PO was a bit of a hacker. I've already started redoing some of the work which wasn't done correctly before. I've even had to replace the turbo, as the old one's impeller was starting to hit the side and dump oil into the manifold :( .

Ideas?

Not sure if this applies, but when I got my 240D I noticed my passenger side heat would never turn off. I looked up the part and found someone mentioning buying a cheap valve from the hardware storethat you could put to block both vents during the summer months. I went to look and found one was already installed, so I just turned off. On mine it's right on the firewall under the hood in front of the passenger seat.

You're describing the "monovalve". It's located between the two firewalls just to the inside of the battery on the passenger side. You may not see it because of the hoses that cover it. It has a round stainless steel top and outside this top is a flange with four screws.

Be careful removing the screws. If you drop one, be prepared to go to China to retrieve it.

When all four screws are out, the piston and diaphragm can be removed. Check for any tears in the diaphragm. It's the most common culprit. If you have a tear report back and we'll tell you where to get a replacement.

If the diaphragm is OK, then further tests of the valve are necessary to determine if the valve iteself is the problem or the CCU is the problem.