Need help with radiator fan on a car?

the car is a 2002 mazda protege5 and the cooling fan will not kick on. the car will overheat but the temperature gauge will not go up past normal operating temperature. i have replaced the sending unit and it has done no good. i am planning on testing the fan right now, but i seriously doubt that is the problem. is there another sending unit? could it be an ecu issue?