Moffat Fridge Temp Problem

I have a 30 year old Moffat fridge that has a temperature regulation problem. The fan for the cold air transfer duct from the freezer compartment to the main compartment is always on. This causes the vegetables, fruits and even milk to freeze solid. I think there is a problem with the thermostat that does not sense the main compartment's temperature correctly and turn off the fan. Where is this thermostat located?

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