Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Separate the inline mains connector to fan assembly

Measurement:

Test 1.
Measure for resistance across the black and blue wires which go to the fan.
Expected resistance 1 Mohm or greater.
Test 2.
Measure for resistance across the black and earth wires which go to the fan.
Expected resistance greater than 1Mohm.
Note.
1. Ensure a good connection is made or misdiagnosis will occur.
2. Resistances may register as O.L on the multimeter, this would indicate a resistance greater than 1Mohm.