If you get good heat on max but no heat in other positions, the monovalve is functioning properly.

The problem is either the CCU or the inside cabin temperature sensor. The CCU bypasses the inside temp sensor when the temperature wheel is at the click stop. I'd check the sensor first. Maybe it's dead.

.... And people laughed at me when I wrote that MB has chronic a/c and air flow problems.

jeff
1991 300d, 100k, with a/c fixed

when applying the 12v to the monovalve,just touch it and get off, manual cautions about damage if voltage is applied permanent. this is from memory, check me out.
larry perkins

Thanks. I haven't had a chance to look at the car again, been too busy mudding my drywall. This remodeling is killing me. But, I'm getting pretty good at doing corners now.. lol

Just joining in to comiserate. Mine is more of an intermittent problem right now, but I've bookmarked this thread for future reference.

__________________

1980 300TD-China Blue/Blue MBTex-2nd Owner, 107K (Alt Blau) OBK #15
'06 Chevy Tahoe Z71 (for the wife & 4 kids, current mule) '03 Honda Odyssey (son #1's ride, reluctantly) '99 GMC Suburban (255K+ miles, semi-retired mule) 21' SeaRay Seville (summer escape pod)

Thank you Brian Carlton. Me, being the dummie I am, replaced parts with ones I thought were good. Turns out, my "good" monovalve's solenoid would not energize. The "new" one I have, I applied voltage to and it clicks just fine. Seems like the heat varies with temp dial now, though I didn't take it on the obligatory test drive yet.

NOTE TO SELF: Test parts before installing... Boy do I feel

My MB 250D-92 had the same probs,the air from the vents was hotter then hell...
Monovalve should always have 12-14 V on the middle pole of contact, and the electronic circuit grounds the valve when it closes....intermittent.
The temperature on the air depends of the time ratio the valve is open/ closed.....so the walves should "klick" intermittent when itīs functioning...
If you not have 12v on the middle pole with ignition "on", check the fuse....

Excuse for my bad English, im one of the Swedes reading this exxelent forum =)