Defrost cycle controller

A defrost cycle controller for a freezer system including a compressor whose operation is activated by a thermostatic switch and a defrost heater whose operation is activated by a bimetal switch, comprising:

• a relay operatively connected to mutually exclusively couple the compressor and the defrost heater to a power supply;
• a first signal line providing a first signal indicative of the operating status of the compressor;
• a second signal line providing a second signal indicative of the operating status of the defrost heater;
• and
• a microprocessor operatively coupled to the first and second signal lines and to the relay to control energization of the relay and to select coupling of the compressor and the defrost heater to the power supply, the microprocessor being programmed to sense the first and second signals and to vary the length of intervals during which the compressor and defrost heater are coupled to the power supply, the microprocessor being programmed to couple the defrost cycle heater to the power supply after preselected decreasing continuous compressor run periods as preselected increasing cumulative compressor run times are reached.

A method of reducing sensitivity of a freezer controller to power outages, comprising the steps of:

• providing a freezer controller which is configured to control operation of a compressor and a defrost heater to monitor demand for the operation of the compressor and the defrost heater via status of a thermostat and status of bi-metal switch powering up the freezer controller;
• after a predetermined interval, determining the status of the thermostat;
• if the thermostat indicates need for cooling, setting compressor run time to a first reduced predetermined value;
• if the thermostat indicates no need for cooling, actuating the defrost heater and after a predetermined time period, setting the compressor run period to a second predetermined time period.