No power to furnace.

[NJC]

1983 gas Lennox that won't start. No power coming to furnace although 120V at the electrical panel from furnace breaker.

I wiggled the breaker around and it still maintained voltage. I must be missing something because I doubt the fault is in wire from panel to furnace.

 

[brianl703]

Furnace power switch off or 24V transformer broke.

 

[NJC]

I'm checking the hot black wire coming in to furnace and prior to 24V transformer. No switch that I can see.

 

[lewdwig]

Could it be a thermostat issue?

 

[NJC]

I shorted wires on back of thermostat and nothing. But as mentioned I don't have any power coming to furnace.

 

[andyd]

reset button on the pump motor?

 

[brianl703]

Furnaces are required by code to have a power switch, it's often a toggle switch mounted near the furnace.

 

[duaneb9729]

sounds like a blower door inter lock switch isnt made or its broken, and thats very rare on a lennox, if you remove the blower compartment door, there is a push in switch that normally is pushed in when the door is on, you can ohm the switch to see if it works. or just press it in and see what happens.

of course the thermostat needs to have a call for heat and the power switch needs to be on.

as far as the electrical code goes, no switch is required on the furnace as long as the electrical panel is located in the furnace room.

if i can help further just im me. repairing furnaces and a/c's is what i do for a living

 

[brianl703]

It sounds like he's checking the incoming power wire before it even hits the blower door interlock, which is why I suggested that the service disconnect switch might be the problem.

 

[duaneb9729]

some how i missed that completely, the switch on the sides do go bad. The lennox blower door interlock switch is made out of metal and is very high quality, the other manufacturers use a plastic switch.

 

[NJC]

Originally Posted By: duaneb9729
sounds like a blower door inter lock switch isnt made or its broken

as far as the electrical code goes, no switch is required on the furnace as long as the electrical panel is located in the furnace room.


There is no switch - 1983 and prior to required codes I guess. Also it does not have a safety override for door. Here's what I'm dealing with.

120VAC supply lines from electrical panel coming in.

And no voltage on the supply lines.

 

[brianl703]

Is it possible that the furnace breaker is mislabeled, and another breaker is actually connected to the furnace?

Where does the BX (armored) cable from the furnace go? Does it go into a junction box?

 

[duaneb9729]

cant get any simpler than this furnace, for heat tonight you could plug it into an extension cord then figure out the wiring to the panel later

 

[NJC]

Brian, I followed electrical supply line as far along the joist (it's located in the crawl space) until it disappeared into wall and couldn't find a junction box nor a spot where it might have shorted.

And to eliminate mislabeled breakers, I tested them all at 119V. I didn't test the subpanel because I assume all main panel breakers would feed into it.

 

[duaneb9729]

test the subpanel also


was this furnace installed in an older home?

or was your house built in 1983?

the reason why i ask is sometimes they had a fuse and a switch on the side of the panel, and the fuse isnt always elimated when they install the new furnace. (in minneapolis mn that is)

 

[brianl703]

Originally Posted By: NJC
Brian, I followed electrical supply line as far along the joist (it's located in the crawl space) until it disappeared into wall and couldn't find a junction box nor a spot where it might have shorted.

And to eliminate mislabeled breakers, I tested them all at 119V. I didn't test the subpanel because I assume all main panel breakers would feed into it.


The armored cable is probably continuous to the breaker panel. Is the panel in a finished wall or can you see where the cables enter it? It's probably going to be the only armored cable connected to the panel, I would expect the other wiring to be romex.

 

[NJC]

Guys, there WAS a wall switch on the stairs going into crawlspace. I had missed it when tracing back to electrical panel because it was behind tennis rackets and lifejackets. It was initially taped in the ON position but the repeated hanging on "accesories" on the wall had broken the tape.

Thanks again for all your help, patience and expertise. Did I mention there was no switch??

 

[duaneb9729]

not that we recall! smiles!

 

[duaneb9729]

glad you got it fixed though!