Hi i have a 89 rs 305 and i cant get the fan to kick in when the car gets to operating temp i have replaced the relay,fan switch(right side of motor), temp sensor(on thermostat housing), and gauge sensor(left side of motor) and I have also checked the fuse and replaced the fan motor the only way it comes on is if i switch the Ac on to max.........I am at a loss Please help!!!!!!!!!!Please!!!!!!

Since it works with the AC on, the relay and fan are good. Check for a break in continuity somewhere in the green with white stripe wire from the fan switch to the relay. If you ground that wire from the switch with key on, the fan should run. If it does run that way the fan switch is bad or not connecting to the wire connector good enough.
And what do you mean by operating temp? It won't come on until around 220 degrees unless you get a lower temp switch