Hi Friends:

I tried to turn the heater on in my 300SD today and it just blew cold air. The only time that it blew warm air was when I turned on the defrosters. Any suggestions? I recently had the radiator flushed. The car does not run hot and I don't think that I have any vacum leaks.

Thanks,

-George

__________________
'81 300TD (White) 225,000 miles
'85 300SD (Burgandy) 239,000 miles
'86 300SDL (Silver) 340,000 miles

Check Monovalve..............and make sure Auxilliary water pump is working and not frozen up.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

I would start at the monovalve. It is the easiest and most likely culprit.

__________________
'85 300SD (formerly california emissions)
'08 Chevy Tahoe
'93 Ducati 900 SS
'79 Kawasaki KZ 650
'86 Kawasaki KX 250
'88 Kawasaki KDX200
'71 Hodaka Ace 100
'72 Triumph T100R

Thank you for the assistance.

-George

__________________
'81 300TD (White) 225,000 miles
'85 300SD (Burgandy) 239,000 miles
'86 300SDL (Silver) 340,000 miles

Since the heat works when in the "defrost" mode, sounds more like a control problem than a monovalve problem. To rule the monovalve out, try disconnecting the wire at the top of the monovalve. Without power to the monovalve, you should get full heat regardless of temperature selected. That will confirm that the monovalve is opening and that the heating system is basically working. If that is the case, your problem is likely with the auto climate control.

Since you indicated that you just flushed the cooling system, the problem could be that you have some air in the system. But if that were the case, you would not get hot air when "defrost" is selected. But you might confirm that your coolant level is correct.

Check also the cabin temp sensor and the aspirator motor.

Sixto
95 S420
87 300SDL