Refrigeration control system with self-adjusting defrost interval

A method of adjusting the period of a defrost interval in a refrigerator comprising:

• providing a sensing means for providing an output signal representative of the temperature of a refrigerator compartment;
• and a thermostat means for providing control signals indicative of the refrigerator compartment;
• continuously comparing the output and control signals for detecting a parameter directly relating to and representing the time period of a defrost operation in the refrigerator;
• continuously verifiying the operability of the sensing means and thermostat means;
• comparing said parameter with a source of signals representing predetermined defrost period limits, said period limits comprising a plurality of preselected defrost operation periods including a preferred period and non-preferred periods;
• generating an output control signal in response to a predetermined relationship between said parameter and said source of signals;
• and,
• adjusting the defrost interval in response to said control signal when the defrost operating time falls within a non-preferred period said adjusting comprising setting the interval to a preselected minimum base interval when the defrost operation time period is greater than a preselected maximum non-preferred period;
• decreasing the interval by a preselected adjustment time period when the defrost operation time period is greater than the preferred period and less than the maximum non-preferred period;
• repeating the defrost interval when the defrost operation time period falls within the preferred period;
• and, increasing the interval by the preselected adjustment time when the defrost operation time period is less than the preferred period, said increasing being limited by a maximum base defrost interval period whereby the defrost interval is maintained within a preferred preselected time period.