Abstract: A blower motor failure is detected by a sensor/switch that opens at a first preset temperature level and automatically resets for the next cycle. The occurrences of such openings per thermostat cycle are counted and when they reach a predetermined number, the microprocessor causes the system to lockout from further operation, thereby preventing the temperatures from reaching excessive levels. In order that the same system may be used in a horizontal furnace installation where the first sensor is less responsive because of its location, a second sensor, of the manually resettable type and having a preset temperature level for opening which is higher than said first temperature limit, is employed to thereby lockout the system.

Abstract: A furnace which normally operates from a residential AC power source is adapted to operate on auxiliary DC power by changing the normal control function to substantially prevent the furnace from operating in the high heat mode during periods of auxiliary power use. Relays can be used to automatically connect the emergency power and to effect the change of the control function.

Abstract: A microprocessor control determines, in the course of initiating a heating cycle, whether the blower is operating in the continuous mode, and if it is, the control prompts the blower to be turned off prior to the ignitor being turned on. In this way, the blower and ignitor are never on at the same time and the instantaneous total current draw is limited to thereby reduce the occurrence of burned out fuses or circuit breaker trips.

Abstract: A two-stage gas furnace control system automatically shifts into a high fire only mode if, in two consecutive low fire heating cycles a limit switch is tripped to indicate that a gas valve is stuck in a high fire condition. In this way, continued operation is allowed to proceed in a safe manner. Provision is also made to lock out the system from further operation if, while in the high fire only mode, the limit switch is tripped in a predetermined consecutive number of cycles or if, while in a preemptive low fire only mode, the limit switch is tripped.

Abstract: A variable speed motor is regulated responsive to the load torque acting on the blower wheel. The load torque acting on the blower wheel is determined by means of a coast down procedure in which the motor is briefly de-energized and the rate of angular change d.omega./dt is determined. The load torque acting on the blower wheel can be determined knowing the moment of inertia and d.omega./dt. The average motor RPM during the coast down is then related to a torque value where an RPM vs. CFM relationship has been empirically determined for that blower wheel. A microprocessor then computes the final motor RPM necessary to achieve the desired air delivery (CFM) using the fan law equations.

Abstract: Provision is made for sensing when the gas valve relay contacts are welded, or stuck, in the closed position and for responsively turning off the inducer motor when that occurs. This in turn causes the pressure switch to open to thereby cut off the power to the gas valve and cause it to move to the closed position.

Abstract: A furnace having the capability of operating its blower continuously is provided with means for automatically shutting off the blower at the beginning of a heating cycle and for resuming the operation thereof only after a predetermined time has elapsed to allow the heat exchanger to heat up to a temperature that exceeds the dew point of the flue gas, to thereby reduce the occurrence of cold spot corrosion in the heat exchanger. Provision is also made, in a two speed blower system, for operating at a lower speed during continuous mode and heating cycle operation, and for operating at the higher speed during the cooling cycles.

Abstract: A self-correcting control system and method is provided for a furnace to correct certain operating conditions that exceed normal limits. Upon sensing insufficient air flow as a function of the pressure drop across the heat exchangers, the control system and method cause the inducer motor to increase in speed, thereby to increase the flow of combustion air. Similarly, upon sensing that the flow of air to be heated exceeds a predetermined temperature, the control system and method will increase the speed of the air blower to increase the flow rate of air to be heated through the furnace, thereby resulting in lowering the temperature of the air to be heated below the predetermined temperature. Upon sensing a gas flow leak through the gas regulator, the control system and method will recycle the gas regulator to properly seat a gas flow control valve therein. If none of the self-correcting features correct the particular occurring problem, the control system and method will shut down the furnace.

Abstract: The control system of an induced draft furnace includes a provision for turning on the inducer motor when a flame is sensed outside of the normal sequence of a heating operation. In particular, if the thermostat is in the off position when a flame is sensed, the inducer motor is turned on to ensure that sufficient combustion air is provided to the burner so as to forestall the occurrence of flame roll outs in the event that the gas valve is stuck in a closed position.

Abstract: The power output of a variable speed motor is limited to a safe level by determining the maximum allowable speed corresponding to a maximum power output limit over a range of load conditions and then maintaining the speed of the motor below those maximum allowable speeds at the particular load conditions existing at the time.

Abstract: A self-correcting control system and method is provided for a furnace to correct certain operating conditions that exceed normal limits. Upon sensing insufficient air flow as a function of the pressure drop across the heat exchangers, the control system and method cause the inducer motor to increase in speed, thereby to increase the flow of combustion air. Similarly, upon sensing that the flow of air to be heated exceeds a predetermined temperature, the control system and method will increase the speed of the air blower to increase the flow rate of air to be heated through the furnace, thereby resulting in lowering the temperature of the air to be heated below the predetermined temperature. Upon sensing a gas flow leak through the gas regulator, the control system and method will recycle the gas regulator to properly seat a gas flow control valve therein. If none of the self-correcting features correct the particular occurring problem, the control system and method will shut down the furnace.

Abstract: A furnace is operated such that the air-fuel ratio and the temperature rise are maintained constant so that the efficiency remains constant over the range of operation.

Abstract: An adaptive motor control for a furnace with or without an evaporator coil determines and delivers the desired CFM for each thermostat cycle. Specifically, a circulating air blower driven by an ECM is initially set at a known duty cycle for each thermostat cycle and the delivered CFM is calculated. The RPM necessary to deliver the desired CFM is then determined and the ECM is set accordingly.

Abstract: An adaptive microprocessor control system and method provide a low heat mode and a high heat mode of a heating cycle in a furnace dependent upon the performance of the previous heating cycle. The duration of the low heat mode and subsequent high heat mode period is a function of the previous low heat mode duration, previous high heat mode duration, and the time period between the end of the previous heating cycle and the beginning of the next heating cycle. The control and method utilize a single-stage thermostat for providing the dual rates of heating.

Abstract: A furnace having a burner fired heat exchanger with a flue gas passage and a heated air passage, a blower powered by an electric motor for circulating the heated air and an electric control circuit with a normally closed relay connecting the blower motor to the power source, the relay being controlled by a "Schmitt trigger" connected to a timing combination.

Abstract: A combination thermostat and blower speed control for use with an air conditioner for both heating and cooling air which is circulated through an enclosure by a multi-speed blower.The control has a system switch for selecting either a heating or cooling mode of operation and a blower speed switch for selecting either automatic blower operation or continuous low speed or high speed operation. The combination thermostat and blower speed control has a built-in override such that when the thermostat senses a cooling need and the control is in the cooling mode of operation the blower will operate at high speed notwithstanding the selection of the blower speed at the blower speed switch.