I have a York Diamond 80 with a White Rodgers 50A50-241 controler. A few days ago I noticed the fan would continue to run after the A/C unit shut down. I had to shut the power off to the unit. The next time it ran, same thing. I switched to heat and the same problem. After the burner shut down the fan continued to run for 20 minutes. The only way to stop it is to shut the power off. Today I found that it runs even with both the thermostat heat/off/cool switch in the off position and the fan switch in the off position. I have to shut the power off to shut the fan down. When the unit is running, the diagnostic indicator light is flashing continously. According to the label on the controler, that means "Flame - No call for heat". What do I check next?
It means the controller is detecting a flame. if the burners are not on you will have to call a tec. to trouble shoot. if you have put the thermostat to off you have disconnected 24v back to the furnace. if you do have a flame (and I don't think you do- because you have not say you are too warm) look for a short in the R and w wire back to the furnace.
Disconnected the wire from the W terminal of the thermostat, and fan stopped. Looks like it is the thermostat. I will change it tomorrow.