Air conditioner gave up a couple of months ago, have had to take care of other problems first, now I need some help with this one. Blower blows hot air in all settings, even on vent without the A/C running. I've checked the mono valve, rubber seals look good. I don't know if this is related, but I'm also experiencing some vacuum leaks, however they started well after the A/C gave out. Vacuum leak symptoms are intermittent and are as follows: engine runs on for several seconds after ignition is turned off; door locks do not activate. Again, the vacuum problems do not occur every time I shut down the engine or lock the doors (BTW - door locks always work when engine is running), and they did not start until well after the blower started blowing hot air, so I don't think the vacuum problems are causing the hot air.

Worst case scenario (if seals, compressor and hoses are fine) is that you need a new evaporator core. Cost is around $220 to $360 depending on where you purchase, and for what model. Only the compressor is more expensive...

The cost of the unit isn't so bad, but the labor is. Installation requires a complete removal of the dashboard and console, since it resides directly behind the front console panel. The evaporator's duty is to draw out hot air inside the passenger compartment, hence its location.

I had to have that replaced on my 300E a couple of years ago because mine had been also blowing hot air (less than a week after getting it recharged at the local Jiffy Lube). The final tab + labor came to $1800. Fortunately I had an aftermarket warranty that covered this, so I was only out $250.

Find a good air conditioning shop to troubleshoot the cause, but I would leave the installation (and subsequent dashboard plundering to the MB experts...Good luck!

Thanks for the info on the evaporator, but if any part of the A/C system were faulty, I would think that the blower would still put out cold air on "vent" mode. Because I get hot air on ALL settings, including the vent, I'm quessing that it has more to do with the cars inability to cut off the coolant flow to the heater/blower. But I don't know what to look for after checking the mono-valve. Maybe the climate control system/thermostat?