How can I check the electric cooling fans? I've never had them come on without the air being on. Now that my air has conked out, how can I test them to be sure they are not the culprit? New resistor was installed in April by Stuttgart South in Nashville

electric cooling fans are for the aircon only when switched on they come on

The aux fans come on high speed when the coolant temp reaches 105C.. can be tested by removing the connector on the blue 2 wire switch on the thermostat housing. They will come on when that circuit is open.
The a/c uses the low speed fan [ pre-resistor circuit ] and comes on when the high side pressure of the a/c reaches 20 bar.... that can be tested by jumping the high pressure switch at the drier/reciever
Two different circuits using the same fan/fans...

this depends on if it has a viscous fan

It does
He has a 201.029 w/103 engine

Also,he already had the preresistor changed out , so that indicates dual fan circuits ...ECT/AC........

thanks...now, where is the thermostat housing? do you mean the coolant thermostat housing(I know where that is) or something different...sorry, mb's are still quite new to me. VW's and Chevy's I'm used to.