All: I've been writing from time to time to tell you abou the furnace problems I've been having. Most recently, I spent megabucks enlarging the supply and return ducts, adding a bypass damper, and adding a return duct. The house is much warmer, and the unit runs much quieter. It still goes off on limit, but not as often as before all the ductwork was done. Also, the fan continues running on occasion, but not as often as before all the ductwork was done. At this point I don't know what else to do about the limit problem, and as far as the fan continuing to run I'm guessing that it's the fan relay which, I understand, is part of the control board and therefore, the whole control board has to be replaced if the fan relay is the problem.
My question this time...how likely is it that the fan relay is the problem? A tech suggested that even though I had the control board replaced once before, it's possible that the overheating problem going on so long may have affected the control board in some was as to cause the fan relay to malfunction. I am not a hvac person. His explanation sounded plausible, but does it make sense from a hvac perspective?
Thanks for the info.