Electric fans burning out the fuses

[BAsque1]

Ron: Update tested both fuse holders for ohms, no reading, tested the fuse holders for amperage, car was off fans off no reading. Turned the car on repeated above same results. Another friend retired automotive teacher feels that is either heat or slow high amperage. No breaks on any of the lines, checked all connections ok, this is a mystery. Fans run fine at the right temp what else could cause this???? See the pictures of the two fuses burnt.

[patrickt]

Originally Posted by BAsque1

No breaks on any of the lines, checked all connections ok, this is a mystery.

No, it's not a mystery. It is either an intermittent fault to ground along the circuit, or the increased heat on the air and the fans themselves results in current above the fuse level. Invest in an inductive ammeter and compare your amp readings at the fan when the engine compartment is nice and hot and see what sort of amps the motors are drawing. If that doesn't tip you off as to the problem, then run a temporary new circuit from the fans themselves directly to the battery and fuse the line at the same amp level. That will eliminate a funky intermittent ground out along the existing line. If the new line blows its fuses as well then there is a problem with the fans, if it doesn't then there's a flaky short on the existing lines to the fan. But remember, when an electric motor starts up you get a huge start-up surge of amperage because of the field that is created. If the fan has trouble getting going, then that can blow the fuse. Anyway, that's how I'd diagnose it. Any electrical problem that happens consistently is easy to find. It's the ones that only occur randomly that are the hardest.