While on uphill climbs my dash vents are putting out extremely hot air. Even when the climate control is turned off. '92 190E 2.6L.

You probably have a vacuum leak somewhere.

My 1991 190E 2.6 does the same thing, but I’ve isolated its exact conditions. The heater (side and floor vents) comes on when the engine gets warm. That’s gets warm, not is warm. How it can tell its a change in temperature and not just the temperature is beyond me. Once the temperature stabilizes the heater goes off. And its only when the normal heating button is pushed when its starts getting warm. If any other button is pushed the heater doesn’t come on, but once it does come on no button pushing will turn it off. When I see a hill and think of it I push a different button. Because its related to the climate control button position I think its the climate control’s fault. Somewhere here I read someone’s mother did aerospace electrical soldiering and had her re-soldier stuff that was acting funny and it fixed it. I can do that type of soldiering and have done that same thing at work to cure similar “funny” problems. So someday, probably when it gets warmer, I’ll dig it out and re-soldier it.

I have the climate control set to OFF when this happens. It's very hot air! It can totally overide the airconditioning when it's on. (sorry to those with snow etc.) I close all the dash vents to keep it from burning me up.

On a similar note, When my sunroof is popped open for a little air the dash vents allow fresh air in while the climate control is set to off.

Steve