I've got a 91 300SE and NO HOT AIR will come out of the vents or onto the floor and it's starting to get cold around here. It blows plenty of outside ambient temp air through.

If I press the defroster button, plenty of hot air comes out of the upper vents.

I read on another forum that the Monovalve might be the problem so I changed it over the weekend but that did not fix the problem. I whipped out my handy tester and checked voltages going to the monovalve and indeed they would change when the button was pressed on the dash which leads me to believe the monovalve was not the problem.

Currently it seems like the CCU might be the problem and I was wondering if there's anything else I should try before replacing the CCU and if I do have to replace the CCU can anyone give me some instructions on how to get started. In addition I plan on having this car for a while so a nice shop manual would be in order - recmmendation on where to buy one?

I must admit the Benz is a little intimidating by not exposing much in the way of screws etc to remove panels. Should I be working from the passenger or the drivers side to remove the center panel to access the CCU panel. I have another CCU sitting here and am ready to change it if need be.

thanks in advance!

- jeff