I have a ford taurus that the cooling fans will only run when when the ac is on 2002/ engine 3.0 efi/

Radiator cooling fans not working ?

Do you know for a fact there is no air in the cooling system and it is full of liquid coolant ? Are the fans coming on with the ac and when the engine reaches 220 degrees ?
Is it possible the water pump is failing internally ?

first check that the fuses are present, and not blown. Test all of the fuses. rarely a relay goes bad, but you could swap the radiator fan relay with the ac clutch relay to verify it's ok. Then check for power and ground at the connector for the fan motor with the engine on, at operating temp., and with the ac on. If you have at least 12 volts between the two wires on the connector, then buy the fan.

CHECK TO SEE IF COOLING FAN IS RUNNING.IF NO CHECK COOLING FAN FUSE AND RELAY.THE COOLING FAN NEED TO BE RUNNING WHEN AC ON BECAUSE AIR CONDITIONER PUT A LOAD ON ENGINE.COOLING FAN KEEP RADIATOR AND AC CONDENSOR COOL.FAN NEED TO RUNNING.

About the only thing that you didn't list is the cooling fan. Are you sure that it's working properly? Drive the car until the engine starts to get hot. After awhile you should hear the cooling fan come on. After you have driven the car for a while, park it and open up the hood. If the upper radiator hose is almost too hot to touch, then check to see if the coolant fan is running. If it isn't, then turn the AC switch to "AC MAX". If the fan still doesn't come on, then a malfunction is indicated. Try to locate the fan control relay and swap it with another relay that has the same part number. Use a relay that will allow the engine to run. Allow the engine to reach operating temperature and see if the fan comes on after switching the AC switch to "AC MAX". If the fan now operates, then replace the relay. I hope this is helpful to you. Thank you for trying Fixya.com. If this does not solve your problem, then post a comment and I will respond by getting into more advanced diagnostics.

How long does the fan run after you turn the engine off? It is normal for the fan to run until the engine temperature is reduced. But if it doesn't turn off at all, then I would check the fan thermostat, it is probably bad.

Making sure the fluid level is up, and there is no leaks in the cooling system, then you must have a circulation problem, Check the thermostat and water pump.

Cooling fans only run when the temp,of the coolant get to about 215 to 218 degrees,and shut them selves off,when the engine cools down,if they do not cut off,the engine is not cooling down,now,if the ac is on,the cooling fans will stay on until the ac is shut off.

The A/C system maybe low on freon. I would have the A/C system checked.

Remove the rad support cover, remove the electric cooling fan and shroud, disconnect the tranny cooler lines, drain the cooling system, remove the upper and lower hoses, remove the rad brackets on top of the rad (one on each side), have someone hold the AC core out of the way and carefully slide the radiator up and out