300SD constant air flow through closed vents
 

the air vent on the lower portion of the dash board near the door handles blowes very hot air in the summer and cold air in the winter, even if the blower is turned off. The blower motor is not running it is like some door is not closing all the way allowing for air off the engine to come blowing into the vent. It sounds like a vaccum problem to me, if anyone else has an idea about it or has had a similar problem please let me know. It is on a 1982 300 SD (126 Sedan)

Dont know if this is any help but I had a problem with cold air coming through my center vents. I took a welding rod with a hook bent in the end and with a SMALL flashlight in the other hand, reached in and closed the vent. Take a peek in and see if you can do that which will keep you from freezing for now:D

Yeah, sounds like a vacuum control prob. Have fun with that one.

To see if the summer hot air is related to the heater not shutting off, take a vice grip and clamp it onto the heater hose coming out of the head at the back of the engine on the drivers side. It's best to use one of the vice grips with straight jaws.