Gas and Oil Home Heating Furnaces - trane xe90 trouble

Hi Everyone,
I'm working on a trane xe90. i am a commercial refrigeration guy and I'm expanding to heating and air.
Burners light for 2 seconds and shut down.
Here what I've done: replaced flame sensor, checked vent and fan, clear and working, ran new ground, reversed polarity just for the hell of it. It was working before so I really rule that out. It had the old board 50a50-474 in it so I replaced it with the 50a55-843. before burners would light for 2 seconds now all I get is 6 flashes and its saying bad ground or reversed polarity. Could another switch be bad giving me this code? What should i try?

Lafam1:confused:

The polarity issue can be caused by caused by the primary and secondary wires on the transformer being out of phase. Make sure the polarity of the supply is back to how it should be (White to neutral, Black to L1) and then try swapping the secondary (load) wires on the transformer. Especially if the new board is made by Emerson. Emerson boards are way picky about polarity. Grounding, and phasing.

The elect. goes to a juction box then to a switch to shut the furnace down. I reversed the wires at the junction box. The led light never came on but the glow plug did as did the inducer fan, just no gas so I assumed that was wrong. Funny though the original way would not even lite the glow plug. The inducer fan would come on then the whole thing would shut down but led would came on flashing the code. 6 flashes.
I then ran a straight ground from the water heater next to it. The main ground for the elect. panels are run to it so I thought it would be a good ground. no luck it reacted the same.
This is a white rodgers board
Any input would be appreciated!
Lafam1:o

By the way I will try switching wires at the transformer
Thanks again
Lafam1

Did you read and follow any instructions with the different numbered board? Sometimes you have to do things with jumpers on different number board replacements.

And did you fasten the new board/ module?, or did you simply let it dangle inside while you test ran the furnace? Make sure it is grounded to furnace.

No sense speculating on potentially 2 seperate issues regarding old board and now the new board. For all we might not know, the old board was indeed bad, and this new one was maybe not set up right. Just saying. They often make more universal boards/modules now, to fit many furnaces, that require different things, to save manufacturing costs and tied up inventory, I'd imagine.

Yes I did fasten the board but its plastic and according to the instructions it can go on any direction and being plastic that cannot be a ground issue. There are no jumpers for anything other than fan delays so it looks like just plug and play!

Lafam1:confused:

Yes I did fasten the board but its plastic and according to the instructions it can go on any direction and being plastic that cannot be a ground issue. There are no jumpers for anything other than fan delays so it looks like just plug and play!

Lafam1:confused:

Sometimes plastic ones have metal grommets in corner holes that complete the ground.

Do you actually have an enclosed module, as opposed to a board? If so, can you read off from left to right, or top to bottom, what all the abbreviations say, where the connections are made on it?

Thanks a good point Ecman I'm going to check that plus do the wire reversing from the transformer as well. I wont get to it till tues probably so i'll post my results then!

Thanks
Lafam1Beer 4U2

hi, lafam1,
don't know if this will help,or if it's too late, but i have the same unit and same problem, one or two burnes light for a few seconds, the unit is in a crawlspace, 4 years old, the burners rusted, blocking the "wicking" channel. changed the burners, and that solved the problem. best price for burners $22. each is patri*t suppl*.
when burners arrive they have a sticky coating on them, i recomend cleaning the channel with a wire brush.
good luck!

Well lafam,

It's apparent that you should stick to commercial refrigeration until you get some training in working on gas furnaces. I hope some poor soul isn't paying you for your doubtful services.

:eek:

??? It's been 3 weeks since he has been around.