Hey Richard,
Sorry to hear about your AC woes. Sounds like the folks you found are either dishonest, or just plain un-knowledgeable abut Benz's. Having said that, this is not a real complicated AC system, if you don't count the ACC unit.
The switch that operates your aux fan, as stated, is on the rec/dryer (sight glass thing), and does not penetrate the freon path. You can first try putting a 10amp fuse into the connectors that plug into the switch. Then just turn on the key and see if fan comes on. Or, try running 12vdc to the fan connectors. If fan comes on, your temp switch is most likely inop.
The aux fan will effect the final cooling of the AC, but it won't keep the air from blowing cool itself. My aux fan is not coming on in the Squash, but the vent temp still hits 41 degrees.
Report back and good luck

__________________
Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John