I have a 2006 MB CLK350 Cab. I needed to have the AC recharged, and the dealer said it had a leak, and that the entire compressor, expansion valve, receiver drier needed replaced and to replace the AC service valve that was leaking for a cost of $2,000. The did put in new coolant, and I ran the AC on the way home. The passenger side worked fine, but the drivers side put out warm air. I ran the AC for several weeks and slowly the passenger side got cooler and cooler until the coolant ran out. Could it be that they just need to fix the leaking service valve and have the coolant replaced again? Another article also mentioned checking a Duo Valve that controls the coolant going to each side. I truly believe that the compressor works fine, and hope to get a more affordable solution. THANKS!

 

Alright.. so it seems like you have 2 issues..
#1 if the refrigerant in the a/c system is low you can have different temps coming out of the vents with the a/c on. I would fix the leak on this first. Unless the refrigerant in the a/c system is black and full of debris, then there should be no reason to replace the compressor unless it has failed. The clutch could be failing, but on some of the a/c compressors they are not serviceable. Did they explain why they wanted to replace so many parts? Lastly, they do recommend replacement of the receiver/drier in the a/c system if it has been opened for repairs.

#2 the duovalve is a common failure and can also cause different temps to blow out of the vents if it is failing internally. The duovalve controls the amount of engine coolant that flows into the heater core to keep it from freezing over into a giant ice block while using the a/c. This also can do the opposite and cause no heat to blow out of the heater if it sticks shut during the winter.

Find someone to properly diagnose and repair the a/c system first and then check to see if your duovalve has failed.

 

I have an old school friend who believes in blowing the AC twice or thrice in winter and the same for heat in summer. Said it keeps things lubricated out of season. I can't prove or disapprove so I do it anyway, figure it won't hurt anything anyway in my 97 Camry, been ok so far. Does this line up with your point 2 above?

EDIT:
Is this something you can diagnose? I am in big D and I see you own a shop in Farmers Branch.