OK so my '03 CLK 500 is giving my frost bite on my toes! For some reason, all of the air is going to the feet, when it's clearly set on the dashboard vents. Any ideas what's up?

perhaps some sort of vacuum leak?

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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

It sounds like you've got a faulty stepper-motor. Do you hear any clicking noises coming from the dash area?

No, but sometimes I do hear whistling.

A quick scan with SDS will tell you which, if any, stepper-motors are acting up.