The air conditioning stops working randomly

I have the same issue with my AC ( GL450 2009), I took it to Mercedes dealership and they too are guessing what might be the problem. They wanted to change the Climate Control unit for $1700 and that is not guaranteed that will work. Did you find out what was the cause?

I have the same problem with my 2009 GL 550. Air conditioning is ice cold at times and then just starts blowing warm air for no apparent reason. It does this regardless of whether I have setting on automatic or not. Eventually it may or may not come back to cold air. I took it to a Mercedes dealer and they installed a new compressor and compressor wiring harness. Didn't solve the problem. Took it back and they still couldn't pinpoint the problem. Eventually took it to another Mercedes certified mechanic and they replaced the receiver drier and expansion valve. After nearly $6000 in repairs. It STILL doesn't work correctly. I'm obviously a little hesitant about spending any more money on this, so how certain are you that the climate controller could be the issue? Thanks