I know for a fact that the other switch you are speaking of runs off 12 volt also.Ray LeTourneau said:cjwigley covered one possibility although ours doesn't have a defrost button. It has 2 switches. 1 is low ambient temp and the other is climate control. One of these prevents the interior light from going out when the door is closed and the other warms the metal frame surrounding the freezer in case you are getting condensation that might freeze and keep the freezer door frozen shut. I know for a fact, the one that keeps the interior light on will drain a battery in a day. I'm not sure if the other is run on 12V or A/C ???