W210 blows hot air from left vent
 

The left vent is blowing very hot air while the rest of the car's ac is working fine. Would anyone know which vaccum module on the ac/heater core unit needs to be replaced? I need help soon, please!!

First things to check are your freon level and your duovalve. Both are common culprits for this -- run a quick search and you'll find my recent posts (and other more helpful posts) on exactly the same problem.

I took my duovalve apart and found all to be well. I then added a little freon and the problem was resolved. Pays to try a few other things before you go in for major repairs!

Cheers, John