I decided that the heater element would turn on only when both of the following conditions are met: (1) The hot/cold switch must be in hot position; (2) The fan must be on.
The hot/cold switch actuates a door in the duct that routes the air to the heating element or bypasses the heating element. I mounted an aluminum spacer onto the duct and added a lever switch. Opening the door will press this lever.
Earlier this week, my paper shredder stopped working. I found a couple of limit switches inside of it. This is one of those recycled components.
You can also see my cat's head in this photo.
UPDATE: I think I found out why my shredder stopped working. I found the lever switch to be a bit flaky. I replaced it with another switch from the same shredder. Also, I love my new DAHLE shredder!