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Discussion Starter · #1 ·
Hi,

How much of the furnace's operation is controlled by the door switch?
E.g. can any fans run with it open?
Is the the control board powered down by the switch or is it just one of the safety inputs to the control board?

Thanks
 

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Discussion Starter · #3 ·
I was looking at a neighbor's furnace and saw no LED lit through the viewing hole nor after I took the panel off. I ordered him a new board but then got to wondering if the door switch had been open the whole time (there were three screws missing on the panel). The fan was running before and after I removed the panel. So it's good to know I didn't order a board for nothing. I'll have to check that door switch when I replace the board.

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I was looking at a neighbor's furnace and saw no LED lit through the viewing hole nor after I took the panel off. I ordered him a new board but then got to wondering if the door switch had been open the whole time (there were three screws missing on the panel). The fan was running before and after I removed the panel. So it's good to know I didn't order a board for nothing. I'll have to check that door switch when I replace the board.

Thanks.
Yeah if the fan was running after you took the door off then someone probably wired around the switch or taped it permanently closed. Because the door switch should turn everything off.

This is why you should never trust a door switch to kill power, always verify power is off. I've been shocked several times because of that or someone wiring the nuetral leg to the door switch instead of hot.
 

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A number of different boards show no led light unless there is an internal fault.
The legend on the furnace door should tell you if the led light should be on.
If the legend only lists fault codes and no code for power then
a stat or stat wiring failure could cause the fan to run continuously with no heat and a properly working board would never show an led light.

Many furnace set ups can also include a continous fan operation.
 

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Discussion Starter · #6 ·
The error code table says no LED means Hardware Fault. I don't know what hardware that means. I assumed it meant the board itself so I ordered a new one. I'll know more once I get the new board.

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The error code table says no LED means Hardware Fault. I don't know what hardware that means. I assumed it meant the board itself so I ordered a new one. I'll know more once I get the new board.

Thanks
Then you're probably right. If it said no code meant hardware fault that means bad board. Or at least that's how I'd read it. I think you're on the right track
 
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