Ford Repair: electric cooling fan, coolant temperature sensor, electric cooling fan

Question
My daughter's "93 Ford Escort, 1.9L,w/AC,standard tran.
The electric radiator fan doesn't run except when the AC is activated or Coolant sensor wiring connector is not connected (which also activates the "check engine" light).  Power is okay at the relay. Relay is working properly.  Have replaced the coolant temperature sensor without results.  There is continuity between the plug for the "out" side of the relay switch and the fan plug with the ignition "off" but I lose that continuity to the fan plug when the ignition is "on", even with a hot engine.  Why does that happen?  Is there a fix other than turning on the AC to activate the fan when she is in traffic and the temp gauge starts climbing?

Answer
There are two temp sensors on this engine, one is for the gauge and the other is for PCM input. As I recall one is facing the front of the engine, the other is under the thermostat housing area. You may have replaced the wrong one. I don't have the schematic handy so I'm not sure, going on memory, which tells me one of these sensors is a thermistor and one is a on/off switch. The threads are probably the same, but the function is different. I will try to find a schematic and let you know what else I can find.