Set Appliance State:

Mains Power Off
Isolate Mains Power to appliance
as per TOP's P4
Set Multimeter to Resistance Set meter to measure resistance
Remove 1 connector from the right hand switch (pink leads)

Measurement:

Measure the resistance across the summer/winter switch (right hand with pink leads).
Test 1
With switch in its (OFF) out position - expect open circuit.
Test 2
With switch in its (ON) in position - expect short circuit.