I have rebuilt the front end of my brothers car after he crashed it. Everything went together and i started the car and was waiting for the radiator fans to come on .  They never came on. So i got to searching there is a cooling temp sensor on the thermostat and one on the bottom of the radiator. Im not sure which one controls the fan. I went out and bought a new temp senor for the thermostat housing and put it in. I checked all the fuses related to the fan and swapped the relays out also.  I can remove one out of the two sensor and sometimes the fan comes on.  Any ideas guys?  I have been looking for a factory shop manual to troubleshoot.

Have you tested to see whether the fan works when you put 12 volts to it? If so and it does, start working your way back up the circuits with your voltage tester to see where you lose it (when warmed up)

T stat one looks to be the one. Just replace the relay and switch, they are cheap and not worth a head gasket repair. They only kick on as needed and don't run all that much. It MAY run constantly when A/C is kicked on, that is pretty normal in a lot of vehicles.

Make sure it is full of coolant and not airlocked also.

I did check the fans and they do come on with 12v. On this car there are two coolant temp sensors. Sometimes when I disconnect one the fans come on. I check at the sensor for the 5v power and it is also there. The only other I can think of is that there is something wrong in the ecm.

Does fan come on with a/c? Find the relay and replace it.

If it is a high-mileage POS Honda with a crappy cheap-ass crash repair,

just hot-wire the freaking fan to come on any time the engine's running.

I did this with my cavalier only I replace the  temp/switch in the block with a two wire unit that control another relay that I installed bypassing the factory crap. It turn on the fan any time the temp was above 180 even when the car was park it would run the fan in till  the engine cooled down

After all kinds of electrical testing the fans work. I guess i never got the coolant temp hot enough. The ac wont turn on the fans because the coolant was sucked out in order the replace the radiator support. Im going to get it refilled and the fan should come on for the ac also.