When a fuse detects too much power running through a wire, a tiny piece of metal inside the fuse will break, thereby stopping the power from continuing to run through the wire.

When the top of the fuse is made of glass, many people think that they can look at the metal piece inside and see if it is broken. THIS IS NOT ALWAYS TRUE.

The best way to handle a suspected blown fuse is to simply replace it. If the power comes back on, great! If it doesn't, then you should call a heating and air specialist who is good at troubleshooting.