Switch Isn't the switch just the breaker on the panel? You should have two breakers to a heat pump with electric supplemental. One services the unit, the other services the plenum heater. For my personal unit, I just leave the breaker servicing the electric plenum heater off until it is required - you'll be able to tell when. FYI, Code locally for us, is a cutoff switch is required if the electrical panel is not in the same room as the unit.