Try to help
I'm no expert, but I'm wondering a few things. If you turn your breaker on and replace the fuse and turn the AC on, does it work? Where your 3amp fuse is, is there power to it all time? Could there be a loose connection somewhere from the main fuse panel to the AC. Is it the original AC? If it is that sucker is pretty old. What is the brand and are there parts available for it if you do find a problem? Best of luck!
2021 Momentum 397TH, 2020 Ford F-350 6.7 PowerStroke, King Ranch Dually.