Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector plug from R on PCB

Measurement:

Measure the resistance between connection 67 (Brown wire, air pressure switch connection c) and connection 68 (Black wire, air pressure switch connection nc) at the disconnected plug.
Note: Measurement taken at disconnected plug not PCB.
Replace connector plug after test.