If the door of the Lennox G16 is removed, thus the door interlock switch unpressed and system off. Does this mean that I only need to shut off the AC power from the outside breaker panel and leave the main breaker on? If not, how about I only remove the wall power plug for the furnace?

Other people can still have power while I service the furnace. I need to do some rewiring for my thermostat.

  • The furnace should be on its own circuit. So you should be able to turn off the power at the panel, and not interrupt anybody else in the home. – Tester101 Apr 11 '17 at 20:02
  • somehow, the furnace is not on its own circuit, but the AC is. – user3108698 Apr 11 '17 at 20:28
  • My G16s (I have two) each have a hardwired switch, mounted on the side of the unit, that shuts off the AC power, and the thermostat transformer. This was done by the original installer. The exterior AC compressors have separate circuits, shutoffs and breakers. – DaveM Apr 14 '17 at 2:38

As I commented, my G16s have a hardwired power switch on the side. Or as others suggested, you should figure out which breaker controls the furnace circuit, and turn it off. (You should not have to shut off the main unless you are working inside the panel box itself)

But after looking over the wiring diagram for my G16, it does seem that the door switch does break the AC hot before it connects to anything else (including the thermostat transformer). So if you kept out of the blower control box, you would be safe to work on the thermostat and related wiring.


There's a breaker that feeds the fan junction box in your furnace. There's usually a regular plug in near your blower unit that can be unplugged. This is the circuits that feed power for blower fan and 120/24 volt transformer for the stat

  • It looks like you didn't finish your last sentence. Please edit this and correct it to clear up the meaning. btw, welcome to SE. Be sure to take the Tour: diy.stackexchange.com/Tour – SDsolar Apr 12 '17 at 5:42

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