Not the valedictorian at HVAC school

My mom is a teacher and was doing a summer reading program when we were visiting. As luck would have it, they had a preschool program so Ellie got to go to school too, which she loved. We were talking about one of the teachers because my mom said she wasn't very good*. I asked how that happens, that not good teachers pass their student teaching and college courses. Which I see in retrospect was a stupid question and I realized it as such when my mother's reply was this "weren't there stupid people in your law school class who graduated?" So I know who graduated at the bottom of his HVAC class. The guy who worked on our air conditioner today. It needed some sort of tweaking due to the stupid hail storm we had last month so the guy was here for a bit this morning doing that. And then a few hours later we (or rather, I, it hadn't yet occurred to my husband) noticed that hey - it's 83 degrees in here and the air conditioner hasn't kicked on since......the air conditioner guy was here this morning. A little investigation reveals parts from the a/c unit just sitting there on top of the unit. I have almost no aptitude toward the mechanical but even I know that ain't right. It took them two hours after we called to send someone back to fix it. Not quite fix but just PUT THE FUSE BACK IN. I can understand forgetting something that's not patently obvious but the fuse was on top of the unit and the a/c fuse box was open so I'm guessing an even mildly experienced a/c guy could evaluate that scene and pick out what doesn't belong. Did he need to leave immediately to rob a bank or something? I think we can safely assume that whatever he was supposed to be doing with the a/c probably didn't get done either.

* Side note: my mother's opinion was possibly also influenced by this teacher telling my mom that her sister made $800 at a bachelor party. Of course my mom said "doing what?" Why "dancing" of course.