Is the fan designed to come on during startup?

I was given an old iBook. (It was destined for the dumpster) It does the "freeze after a couple of minutes" if you try to play a game or anything else video intensive. We've re-soldered the offending chip on the board, and checked everything else out. I don't have access to original software that came with the machine. With the back off, I can see the fan never moves at all. Not during start up, or use. Nothing. Should I just try to locate a replacement fan?

thankss