So this is probably common knowledge for some people but I wanted to post it anyway because of how long it took me to find the solution. My radiator fan (passenger side) would not come on while the car was running even if it was over heating. If it did overheat and I turned the car off, the fan would come on. I ended up putting a jumper wire in the connector located on the switch on the thermostat housing with the car running and the fan came on. The jumper simulates the switch closing like it's suppose to. So I replaced the switch and the fan now works. The switch is an ECT (Engine Coolant Tempature) switch.Hopefully this will sometime help someone.

 

That's a standard way to check a thermo switch. Glad you found the problem.

 

How about the other fan ?? the one on the driver side ??

 

I've got no AC, it was all taken out. I had wired it in with the passenger side fan but it's got a bad motor or bearing or something. It would come on but it made some hellacious sounds so I disconnected it.