My 84 300SD blows strong,cold air into the back seat. The slide lever can almost stop the air, but not quite. When it is -30c out this is more than a little annoying. The fan blows through the ducting and must be getting straight outside air. The other car vents appear to work correctly. How can I connect the rear duct to heat???

Thanks for any help.

I don't think you can get heat at the rear vent. If anyone knows how I would like to know for future reference.

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual