Mark A Whitaker

US Patent:

53721209, Dec 13, 1994

Filed:

Jul 23, 1993

Appl. No.:

8/097281

Inventors:

Robert C. Swilik - Indianapolis IN
Mark T. Whitaker - Greenwood IN

International Classification:

F24H 300

US Classification:

126116A

Abstract:

There is disclosed a modification in the control circuitry of a gas furnace having a primary or main limit whereby the primary circuit subsumes the functions of a the secondary or manual reset limit circuit. The control circuit incorporates a microprocessor capable of sensing conditions in the furnace, enabling and disabling the various furnace components. When an overtemperature condition is sensed the furnace is thereupon disabled by a process that executes in the microprocessor and comprises the repeated steps of: sensing if the limit switch is open; determining, in the event that the limit switch is open, whether the limit switch remains open for a period that exceeds a predetermined time interval; incrementing a cycle count in the event that the limit switch has remained open for the predetermined time period; waiting for the limit switch to reset in the event that the incremented cycle count does not exceed a predetermined value, and reinitiating the combustion cycle if the step of waiting was performed; and disabling the furnace in the event that the incremented cycle count exceeds the predetermined value.