My Rheem furnace is showing a diagnostic red flashing light, flashing 3 times
m/n# A0336JK06X PC boerd 62-23599-01

Inside the door you remove to expose the blower you should find a chart that explains the codes. This time of the year the most frequent issue is lack of combustion air or blow back due to fire places. The serial number you gave does not come up on my search, sure you got it all correct?