I have a 1995 Dodge Grand Caravan. I got it used last fall, and haven't used the A/C yet. I recently tried it, and it did not work, but I checked the pressure and it was empty, and as soon as I added a little refrigerant/oil/sealant the system kicked in. I went to fully recharge it today, and found that the compressor is no longer kicking in. I checked the fuse (15 AMP in the under-hood fuse block) and it was blown. I replaced it, but it blew again as soon as I turned on the AC switch.

What things should I check to try to figure out why the fuse is suddenly blowing?

Are you meter savvy? May have a dead short in the clutch. You can check that at the compressor clutch connector. You may have a short to ground in the wire from the relay to the clutch.