Self-correcting microprocessor control system and method for a furnace

In a gas-fired furnace including

• a housing having a combustion air inlet and an exhaust gas outlet,
• a combustion means in said housing in communication with said combustion air inlet for receiving a flow of combustion air and for burning a mixture of combustion air and fuel,
• a fuel supply means in said housing and connected to said combustion means for supplying flow of fuel to said combustion means,
• a heat exchanger means in said housing in communication with said combustion means and said exhaust gas outlet for delivering a flow of a combusted fuel air mixture therethrough, and
• a blower means in said housing in communication with said combustion means and said heat exchanger means for providing a flow of combustion air through said combustion air inlet and said combustion means and a flow of a combusted fuel air mixture through said heat exchanger means and said exhaust gas outlet,
• a self-correcting microprocessor control system, comprising:
• an air delivery passage in said housing for delivering a flow of air to be heated over said heat exchanger means,
• a circulating air means in said housing for circulating a flow of air to be heated through said air delivery passage, and
• a temperature-sensing means in said air delivery passage for sensing the temperature of the air to be heated as it flows over said heat exchanger means and for generating an air delivery increase signal when the temperature of the air to be heated exceeds a predetermined temperature value,
• a microprocessor control means for receiving said air delivery increase signal and generating in response thereto a circulating control signal to said circulating air means,
• said circulating air means further providing in response to said received circulating control signal an increase in circulation of the air to be heated over said heat exchanger means, thereby to lower the temperature of the air to be heated below said predetermined temperature value,
• said temperature-sensing means being further capable of generating an insufficient circulating air flow signal when the temperature of the air to be heated remains above said redetermined temperature value after said circulating air means provides an increase in circulation air;
• said microprocessor control means further being capable of receiving said insufficient circulating air flow signal and generating in response thereto a termination signal to said fuel supply means, and
• said fuel supply means being capable of terminating the flow of fuel to said combustion means in response to receiving said termination signal.