Heater not mixing air- too hot
 

Driving home last night, I noticed that the heater was blowing too hot not mixing air properly even with the temperature dial on minimum. The HVAC buttons work to turn the system on and off. Its just the temperature control thats wacky. Way too hot, had to open windows. It is getting cold up where I am...was 32 degrees this morning. I would appreciate guidance to resolve this. The vehicle is an '84 190D 2.2.

Thanks in advance,
ARVY
1984 190D 2.2
1992 300E