Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove the 3 wire connector from the fan

Measurement:

Fan doesn't have to be removed for this test if access to remove the side panel is available.
Test 1
Measure the resistance between terminal 1 and 3.
Expected resistance 1 MOhm or greater.
Test 2
Measure the resistance between terminal 3 and earth.
Expected resistance 1 MOhm or greater.