Why did you replace a good fuse and then suspect the switch? A fuse is very easy to check.
Guessing won't fix the problem until you get lucky and replace the faulty part. You could easily make a bad situation worse by taking things apart that aren't broken. This is a relatively easy problem to troubleshoot with a multi-meter.
When heating elements fail, the usual suspect is the heating element. If they short, they'll continue to blow fuses every time the switch applies power to the heating element. Usually, heating elements open, so the fuse remains unscathed. The switch is more reliable than the heating element (though any component can fail.)
All of the above is educated guessing, --based on experience. That's where the "trust, but verify" troubleshooting logic kicks in. I try to identify the least reliable component in a circuit (after checking the most obvious - like a fuse) and then prove which part is bad electrically before doing any more disassembly than necessary.
Use a multi-meter to check the back of the switch, or it's connector. The same with the heating element - you should measure resistance across the element. Then you'll know which part to replace, saving time, money and frustration.
If you don't have a service manual and need a remove/replace procedure (with illustrations) and associated schematics with connector pin-outs, it's totally worth the effort to shell out $10 for a full day of access here:
RepairProcedures.com - Providing electronic service information for 1995 to current GM vehicles
CC
