" wrote:

Fuses rarely fail on their own, they are usually an indicator of a
problem elsewhere.

We had some warm weather over the weekend, so I turned the thermostat
off. I asked my son to turn it back on, and I noticed that the fan
switch was set to "On" instead of "Auto."

Would the blower running continuously for a day or two be reason
enough to blow the fuse?

Even without knowing which fuse it was, it's highly unlikely. Any fuse
in the system should be sized for continuous operation.

Pete C.