Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect one of the black wires from the fan thermostat located adjacent to the fan

Measurement:

Measure resistance between the exposed terminal of the thermostat and the screw securing it to the fan assembly.
Expect open circuit (O.L).
Is the resistance measured as expected?