Heater fuse keeps blowing

Hello,

This fuse keeps blowing because somewhere in the circuit there is a short to ground. This happens when a part of the wire's insulation wears off or something else causes a part of a wire or a connector's bare metal to touch the body of the vehicle. When this happens it "short circuits" the circuit, eliminating the resistance that the load, what the circuits voltage was intending to run, would have had. As per Ohm's Law, whenever voltage remains constant(as always is the case in an automobile), if resistance goes down than current must go up. The "short circuit" will allow more and more current to flow until it surpasses the amperage that the fuse can withstand, and, pow, the fuse blows, just as intending, saving an electrical fire, and damage to the components.
I have included your vehicle's HVAC wiring diagrams. Follow the circuit from your fuse and find and repair the short circuit. Get back to us with what you find out.

Thanks,
Alex
2CarPros