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Old 06-15-2010, 08:56 PM
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Cooling fan relay melting

On my 59 Suburban with 2004 5.3 we used a single electric cooling fan. We wired it with 10 gauge wire to a 40 amp relay. After two years the relay melted at connectors 30 and 87. The wire connected to these terminals was also charred. Do I need a different relay? Puzzled

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Old 06-15-2010, 09:07 PM
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You need heavier wire 8 , is the fan still good, the 40 amp relay is good enough . Wire size 10 is good for about 25 amps that would make the wire hot and the insulation soft , remember that fan draws max load and runs all the time ... bigger wire cooler circuit .
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Old 06-15-2010, 09:24 PM
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#8 wire might be better, but that's probably not what caused your problem. Sounds more like the terminals/connections developed a bit of tarnish or corrosion. With a high current trying to pass thru those connections, heat was developed which caused the wire to be burnt. Anything that increases the resistance at the terminals will produce heat when current is flowing, and cause reduced voltage at the circuit load (in this case...your fan).
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Old 06-15-2010, 09:29 PM
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My thought is that the relay must have been OK originally if it lasted for two years. To fry the relay and warm a 10ga wire to the "charred" point would take a very high draw, probably more than the fan motor. I'd be looking for a short somewhere.

Does the fan turn freely?
Is there a sticker on it stating amp draw rating?
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Old 06-15-2010, 11:51 PM
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shorts take out the fuse if everything is correct. loose or cheap wire connectors will cause resistance (which is heat)fans tend to draw a few more amps as they age. Every wire I have replaced that fits your description can be traced back to improper crimps or loose/corroded connectors. If you look you will probably find that the wires from the fan motor are 14 gauge. Feed the relay with 10g and put it as close to the fan as possible(shotest possible run of the wires)and fuse it 5 amps more than the fan rating.
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Old 06-18-2010, 10:15 AM
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There is a 2 inch section of 14 or 16 gauge wire my brother used on the fan feed wire to the relay terminal. I'm guessing he used it because the terminal connector can only handle the smaller gauges.
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