300E Auxilary fans and A/C

[TCCBass]

Had the head gasket changed and valve job done in the 300E. WOW what a difference. My question is about the fans. When the car gets to 90deg, one of the front fans kicks on (pass side). When I turn on the A/C, NEITHER of the fans kicks on. Is it the switch on the drier, or is it the fan? I know the way my 300TD works, but am not as familiar with this car. I'm taking it back to the mechanic to have the idle adjusted, but would like to solve this one myself. He thinks the fan is out, but I am hoping for the switch.
1. Is there an easy way to bypass to check the (drivers side) fan?
2. If it is the fan, how difficult is it to change the fan?

Any suggestions would be of GREAT assistance. The car cools fine when in traffic with the A/C off, runs REAL hot with the A/C on.
Thanks!