Brian,

So you would agree with the statement that the reason red-hot air is coming out of one vent and not the other ones is due to a blocked heater core?

RSCarey

That's more difficult to confirm. I don't know the air supply system on the W123 well enough to be sure of this. However, if the airflow leaves the heater core and splits into two paths immediately after the core, it's possible that a portion of the air leading to one vent will be hotter than the air going to another vent.

But, I would have to say that it's a stretch to conclude this without additional data.

I have the same problem in my 115 300D, air from passenger side dash vent, not drivers... and its cold
From the passengers side is lukewarm after the temp comes up... that sucks... I know its a summer car, but BURR
How much fun is it to replace/recore the heater core?

Thanks alot, sorry for the hijack
~Nate

__________________
95 Honda Shadow ACE 1100.
1999 Plymouth Neon Expresso. 2.4 swap, 10.5 to 1 comp, big cams. Autocross time attack vehicle!
2012 Escape, 'hunter" (5 sp 4cyl)

I just climed out from under the Rattlemobile, after a rewarding--and inexpensive--day of wrenching.

After rebuilding the monovalve, replacing the aux coolant pump and ACC controller, I finally got the heater to work by power flushing the entire system. At high pressure (of course not too high) I blasted out another handfull of sandy, rusty, decomposed hose chunks, and grey goo.

Proceeded to do the de-oil flush with detergent. Rinse. Fill. Rinse.

Added citric acid solution, drove across town to pick up some anti-freeze. Dumped. Filled. Dumped. Filled. and so on...

Added new coolant, and now the heater will melt your face off. Operating temperature is five degrees cooler now, and the passenger cabin is thirty degrees warmer.

Thanks to all who contributed to this thread. Without your help, I'd be forced to drive a Yugo.

RSCarey

Excellent. Fantastic outcome.

Help is what we do here.