If you're talking about the fan that moves air up the inside of the bottom half of the trailer behind the refrigerator, it is thermostatically controlled, and won't turn on until the temperature in that area is 110 degrees (as I recall). It's possible that the fan is ok but that the temperature in that area has not gotten high enough to turn it on. Also, there is a 1 Amp inline fuse to that fan that might be blown, which would prevent it from operating. The fuse is near the floor of the fan compartment in my trailer.
I replaced my fan with two, computer chassis fans that move more air, are quieter, and use less electricity than the "Mattel toy fan" that was installed in the trailer. My installation is part of this thread, started by sushidog: https://www.hilotrailerforum.com/f35...rator-fan-261/
I also saw a thread recently where a member replaced his fan with three computer fans. Basically, any 12V DC fan that will fit in the space will work.