1999 Pontiac Montana

Are you sure the fan motors are good? As far as the switch, the sensor can be found on the right side of the engine.

Here is its purpose:

"The Powertrain control module (PCM) controls the operation of the cooling fans. This is accomplished by providing a ground path for the cooling fan relay coils within the PCM. The relay contacts will close and complete the circuit between the Maxifuse  in the underhood electrical center and the fan motors. Whenever there is a fan "on" request, both fans will be running. A coolant temperature switch activates the fan motors. A transducer can also activate the circuit, depending upon A/C request or A/C compressor head pressure to the condenser."

Let me know what you find.