Try running the 12-volt fan on 6 volts and see if it throws enough air, if it's a simple brushed 12-volt permanent magnet motor it will run.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
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