I have a carrier furnace that says reverse polarity in heat. In cool it works fine.
I replaced the control board last year and it worked fine all winter. This year I checked it a week or two ago to make sure it would work OK before I actually needed it in case I needed to order something.
It worked fine when I ran it then (after I turned on the gas valve that the last company I paid to fix the A/C felt the need to turn off.
Now it is getting pretty chilly at night and I went to turn it on and the LED light just blinks rapidly.. According to the cover this indicates a reverse polarity. The polarity is NOT reversed in the 110 coming in to the furnace.
I read another question here similar and the fix ended up being reversed polarity on the secondary 24 volt or something.. Im not sure which wires they mean by that to even try it. If you think that is the issue please explain which 24 volt wires you are talking about.
Thanks

If it used to work correctly, and no rewiring has been done on the unit. I would not touch the wiring as far as reversing.
I would follow the wiring back from the Heat Relay and into the control board. Is their a fuse for Heat?
Sometimes when there is an open in a circuit it will show a reverse polarity.
On open neutral, will many time show as reversed polarity.

I agree with start. If the unit worked, and now it doesn't, and no wiring was changed, it is most likely not actually reversed polarity. Definatley some testing that needs to be done here. If all test prove in order, and you are still getting the code, then you are getting an incorrect code which means you would need a new control board.

It has one fuse on the control board and that fuse is good. All other wiring seems OK. I did replace the thermostat a couple of weeks ago... could the thermostat cause all of this? I am pretty sure I tested it AFTER replacing the thermostat.

On second thought I can get an IMC control board and replace it for 125 bucks.. probably the best option looking at it. I notice a bunch of corrosion on the board (probably due to my drain line clogging up and the water draining out of the a coil housing and running down into the furnace)

If anyone else has a suggestion before I order another board please let me know. Thanks

I would remove thermostat, check all connections, and be sure a screw doesn't poke the control wires.
Now reading the corrosion, replacement would not be a bad thing, corrosion only gets worse.
I would "walk" your leads back from the Heat Element back. Sounds like a 120 volt system. Move leads back 1 at a time and through the board and any relays on board. If you have voltage to an on board relays coil and it doesn't energize, or provide power out. It would just be that relay.