w124 94 E320 wagon climate control

1994 E320 wagon climate control system is blowing hot air from side vents with a/c on at high, low or auto fan speeds. Turning the temperature selector wheel does not seem to affect the hot air output from the side vents. You can also feel mixing of hot air in the center vents with the cold air. The air conditioning compressor is working and cool air is being blown into the cabin. Any suggestions would be appreciated.