Abstract: An adaptive defrost control system of the present invention monitors an amount of current flowing through the defrost heater to calculate the amount of power delivered thereby. The circuit utilizes a thermistor to monitor the temperature rise of the electrical trace supplying current to the defrost heater to allow the controller to calculate an amount of power delivered thereby. A second thermistor may be used to compensate for a change in ambient temperature that might otherwise be attributed to a change in current flow through the power trace. A physical modification to the power trace to enhance the temperature rise characteristic at the point of placement of the thermistor enhances the accuracy of the calculation. A secondary current flow path around the branch of thermistor placement is also provided so as to not reduce the total current carrying capacity of the power trace.

Abstract: A defrost heater relay control circuit having reduced power consumption during a de-energized mode of operation is provided. The relay drive circuit utilizes a series connected capacitor to introduce a phase shift in the AC current waveform such that the amount of real power dissipated in the circuit during periods when the defrost heater control relay is de-energized is greatly reduced. This effectively shorts out the relay drive voltage without generating heat due to real power dissipation through the switched circuitry that disables the relay.

Abstract: An adaptive defrost control method and device for controlling a damper door during a defrost cycle is provided. Before entering the defrost cycle, the adaptive defrost control logic determines if the damper door is open. If the damper door is open, the defrost cycle is suspended until the door is closed. If the damper door is closed, the adaptive defrost control logic activates a barrier between the damper door motor and a power supply so that the damper door may not be opened during the defrost cycle. After the defrost cycle is completed, the adaptive defrost control logic removes the barrier between the damper door motor and a power supply. The damper door may then be opened and closed as necessary. Accordingly, warm moist air from the defrost cycle does not enter the fresh food compartment.

Abstract: An electromechanical relay drive system which prolongs relay life by ensuring operation of the relay in a manner to make and break contact between the contact electrodes at a zero crossing point of the switched waveform. Relay aging and environmental variations are dynamically compensated upon each actuation of the electromechanical relay to ensure proper timing of the energization and de-energization of the relay to ensure switching at the zero crossing point. Additionally, the drive system described compensates for variations in the actual contact operation during actuation for the positive and negative half cycle of the switched waveform. Furthermore, the system of the instant invention alternately energizes and de-energizes the electromechanical relay during the positive and negative half cycles of the switched waveform to prevent metal deposition from one contact electrode to the other.