We were flying west in the afternoon. Me, in the engineer seat, enduring another check ride. The pilot reached up and increased the heat. I informed him I would be happy to use the temp controls on my panel to make him happy because I like happy pilots. He looked back and told me, I can handle it. I thought to myself OK big boy. After the third adjustment I reached down grabbed the autopilot and turned right. After he got us back on course he asked why I did that. I told him the sun was in my eyes and thought a new heading would take care of it. After a long silence he admitted lesson learned.