It would be really odd for the resistor pack to go - those things are built to last. I would bet on the amplifier, which is a common failure if the servo dies.

Another issue might be a vacuum leak or a bad vacuum element or a bad micro switch. The flaps have to be firmly in the AC position for the compressor and fan to come on.

Lastly, DEF should engage the compressor. If it doesn't then you may have a compressor or low freon problem.

Good luck.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe