Hello. I have a York Diamond 80 furnace with a new Emerson S1-33109167000 control board. The problem began when the fan wouldn't turn off even though the A/C compressor had turned off. The original control board had gone bad and was replaced. But, the fan still keeps on running. The led has a steady green flash which the codes list says means that all is normal.I have heard that control boards can be wired so that the fan runs all of the time. Could this be the problem? If so, is there a way to fix this?

Luxair is a division of York so this sheet will work for you.

http://www.luxaire.com/PDFFiles/035-21366-001-B-0208.pdf

NOTE: Check to be sure your thermostat is set to auto and NOT on for fan operation.

Also check the thermostat cable for shorts by removing the GREEN thermostat wire from the circuit board. If after removing the green wire the fan shuts off there is a wiring/thermostat problem. If the fan keeps running then issues with the control board will need to be addressed. NOTE when removing the green wire after you turn the power off make sure it is insulated or tape protected so it cannot touch anything and cause a short circuit.

NOTE: Check to be sure your thermostat is set to auto and NOT on for fan operation.

Also check the thermostat cable for shorts by removing the GREEN thermostat wire from the circuit board. If after removing the green wire the fan shuts off there is a wiring/thermostat problem. If the fan keeps running then issues with the control board will need to be addressed.

Thank you for your help. After disconnecting the GREEN wire from the control board the fan still came on. I know that the old board was bad because I saw where a part had burnt through. I inspected the wiring and it is connected the same way as it was to the old board. When I switch the unit to HEAT the fan turns off as it should. Only when it's on A/C does it run continuously.

It is possible the board is defective or the fan selection switch on the circuit board is not adjusted properly. I make a assumption that this is just a standard system with no added relays etc. I will be back later on this afternoon to answer your reply.

It is possible the board is defective or the fan selection switch on the circuit board is not adjusted properly. I make a assumption that this is just a standard system with no added relays etc. I will be back later on this afternoon to answer your reply.

Thank you. Well, the board still flashes the green heartbeat. The fan selection switch?

The fan selection switch?

You can give that a shot but under normal conditions in the A/C mode the fan should shut off when the ouitside unit shuts off or soon there after. OR when the green wire is removed from the circuit board since that is the usual signal circuit for the fan operation.

Gotcha. Oddly enough, after cycling through heat for about an hour and then turning the unit off for 30 minutes, it's working perfectly in A/C mode. Not sure what's going on here but my fingers are crossed.

See how it goes and post back with the results.

Well, it only works like it should during heat mode. After awhile last night, on A/C the fan stayed on. I'm stumped. The last two techs who came out to my house wanted to charge me an arm and a leg for what they wouldn't tell me. I guess I should find another?

With it working corectly in the heat mode we know that the limit control is not causing the fan to run to get you attention since that is a default setting for a overheat condition. So that is OK.

If you have check all that was requested then I hate to say this but the indicators are pointing to a bad control board. It makes no difference if the board was just replaced or not it still indicates that the board is causing the problem since nothing is left to check. It could be the board was damaged when originally installed? Who knows.