Radiator fan will not shut off

My 2002 Windstar Radiator fan comes on high when I start the car, it will not shut off, The temperature is below freezing, Stays on after the temp gage reads normal.

Start by checking the fan relays. There is a high speed relay and a low speed relay.

After that, at least two things control the fan relays:
1) A/C On
2) Thermistor reading on cylinder head