140 AC problem: heat kicks on driver side
 

Need more help with my '93 500 SEL's AC system. Here is the problem:

1) works fine for about 10 minutes
2) heat comes out of the two driver AC vents. Cool air is coming out of the passenger and rear vents.
3) push the cool air button on the center dash and cool air comes out of the center vents. (Leftmost is still hot)
4) No code failure in the Climate control's diagnostic computer (my mechanic checked this also)

Sometimes the air from the driver's vents pulsates from blazing hot to almost cool. This one has stumped me and my mechanic.

Any suggestions?

Thanks,

John

Check function of heater duovalve.

Same problem on my 1995 S350 (W140). Only difference is that my passenger side vents are the ones blowing hot when they should be cold.

Also causes my engine temperature to go from the normal 80 up to around 100. (Possibly caused by the AC running full blast trying to fight the heat?)

-Jim