I bought this car July with 86K miles. The AC was freshly charged when I bought it and worked fine, but stopped working two weeks later. The MB dealer checked out the system and found nothing wrong; the system started to work again. I drove cross country to AZ, and everything worked well all through the 115 degree summer. I stopped using the AC in fall, but noticed that the system seemed to go on and off once in November when I used the AC (wasn't sure, since it was cool outside anyway). Now the system doesn't work again. I took it to the local dealer, who said I need a new evaporator and expansion valve.

Is there any other switch/control/electronics that could explain the AC problem apart from the expensive evaporator repair? I'm not sure this dealer spent any real time diagnosing the problem. I know the last dealer spent a good amount of time checking out the system and found nothing wrong then with the evaporator. Any advise would be greatly appreciated. Thanks.