2000 Nissan frontier truck with A/C problems

I have a 2000 Nissan Frontier truck and the air conditioning 7.5 Amp fuse blew. I replaced the fuse and it worked for about three weeks. Then it blew again. The blower and the lighted on/off button works correctly, however it does not blow cold air. The fuse now blows once the A/C is turned on. Any suggestions on things to check will be greatly appreciated.[/code]