If all the fans run with the AC on (front and back electrical radiator fans), the fan relays and circuits are good. I would check the radiator thermostat fan switch usually mounted on the engine thermostat housing, using a short jumper wire with spade terminals crimped on both ends, insert that jumper wire in the 2 wire thermostat switch connector and the fan should run constantly with the key on (the first stage rear radiator cooling fan, not the front additional AC operation fan). It's usually the thermostatic coolant fan switch or the cooling fan relay inoperative. Shorting that thermostat housing fan control temperature switch connector with the key on and engine not running should give you 12VDC at the rear engine compartment side electrical fan connector and energize the rear radiator cooling fan with the ignition switch on, regardless if the engine is running or not because the jumper wire is bypassing the cooling fan temperature switch.
Add; The bypass jumper allows you to quickly diagnose the issue by manually energizing the radiator cooling fan, thus putting 12VDC on the connector so you can test the 12VDC on a volt meter at the fan motor connector to determine if the actual fan motor coil its self is defective. This is how us true mechanics diagnose this issue, and can test it in just a minutes time whether its a car or a big rig without chasing fuse diagrams. You will be able to hear the fan relay click when you touch the jumper to the fan control SW connector (engine not started and ignition key in the run position). If you can hear the relay click but get no power, the relay may be the culprit. I'm no fan of replacing good parts, you can get a cheap $15 VOM meter for the price of the relay. Both the relay and temperature control SW are about $15 parts.
See this picture link for the fan thermostatic control SW location - https://ww2-secure.justanswer.com/uploads/FIXITMAN/2010-04-14_174746_120033913.jpg
· 11 months ago