Problem: fan is not turning on in the refrigeration part, freezer is working great, reset the door controls and that did nothing, unpluged the themistor and the fan stays on and freezes everything, Unit seems to be in constant defrost but not sure. I believe the themositor should be a closed switch, and when cold opens, it this correct?

Replaced the main board, the fan, the THERMISTOR FF EVAP sensor. The thermostat, the only part not changed was the thermostat sensor, all parts have to come from the USA and hand delivered, so I am trying to get this working properly, The refrigerator is irreplaceable, We had to have a crane bring it up 8 stories and a dozen men reach out and catch it.... not for the faint of heart.... so I cant just go out and get another one.... got to trouble shoot this one. How do I test the thermostat sensor as this is the only piece that isn't new, or is there a reason the fan is off< the door switches are bypassed during the test.

GE PSB48YSXASS

Parts replaced, 602,608, 609, And the main motherboard

https://www.geappliancep...0/0/0/FRESH_FOOD_SECTION