Mustang Man, with the system operating correctly, there should never be warm air from the center vents. Only floor, defrost or outer dash vents. You might get somewhat warmer air for a few seconds from the center vents as the in car temp sensor measures cabin temperature and switches modes. This is assuming you have auto climate control. Please list the year and type of car in your profile.

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.

Ahh yes, the day after postiung I realized I had forgotten that, (what I get for trying to think late in the day) I am now beginning to think that I don't have the auto system, as I dont have any pushbuttons in my console/dash ( and am now seeing mention of pushbutton units) I only have the two knobs going to firewall mounted split heater valve, and a third knob above that with a snowflake type logo on one side and a line around the knob going from blue to red (which I had thought at first to be a climate controller).

-Chris 80 240D w/617

Does it ever blow hot air? or does it work the same as the front?

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83 300SD Dark Silver Dark brown inside

The rear seat vent never blows heated air unless you live around here in the summer.

It blows strictly a/c or outside vent air. The heat comes from ducts below the seats....keep the floor mats away to get good flow.

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Sam

84 300SD 350K+ miles ( Blue Belle )

I know I got to start trackiing down my vacuum issues as well. 1 more question, the CCU defaults to defrost if the vacuum is bad correct?
Time to get a mighty vac

thanks
Doug

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83 300SD Dark Silver Dark brown inside