I chased the exact same problem on my AC for years with no luck. Went through a couple dozen 30A fuses, and yet the AC rarely would keep working for more than a few minutes to a few hours. I replaced the fan-speed control and the fan motor, and checked all my amp draws up and down the line. Could never read more than 8 amps total and yet the fuses kept blowing. Really frustrating.
Then Jeff Carter suggested I look for the cause to be in the thermostatic control, and that I should gently abrade the points. I did that and it seemed to improve it, but a couple hours of use later I was back to blowing fuses again. I still thought he was probably right and that arcing in that stat unit was where the problem lay. I figured what might be happening was that the points were closing very slowly as the ether in the thermocouple expanded instead of snapping closed quickly - causing a brief (but too long) arcing across the points and a draw over 30 amps just long enough to blow a fuse.
To check the theory, I put in yet another fuse and hit the road again in 95 degree weather for 3 hours. Only this time I operated it by turning the stat to either full OFF or full COLD, and would only make that change with the AC system itself shut off for a moment. I did not set the stat at any partial call for cooling on this trip, and therefore the points did not cycle and could not arc as before. The bottom line is that it worked like a charm and that's the last fuse I've had to put in it. I know now that arcing in the stat is the only explanation.
What I cannot explain is why this would not have been a big problem with ACs back in the day - or what they did about it if is was. But my solution is that this week I am going to put in a relay after the stat. The stat will then only be a low amp signal to the relay, and the relay can do the heavy work. Jeff says there is a 20A breaker on the back of the wiper switch I can tap for the relay power source.
So if my problem sounds like yours, give this test a try. Don't let the system cycle through the stat on a partial-cooling setting and see if the 25A fuse holds.