Refrigeration control regulating temperature and frost build-up

Claim 1

REFRIGERATION CONTROL APPARATUS FOR CONTROLLING REFRIGERATION COOLING MEANS ADAPTED TO ABSORB HEAT FROM A REFRIGERATED ZONE, SAID COOLING MEANS BEING SUBJECT TO FROST BUILD-UP, SAID COOLING MEANS HAVING MEANS ASSOCIATED THEREWITH ADAPTED WHEN ENERGIZED TO DEFROST SAID COOLING MEANS; SAID CONTROL APPARATUS COMPRISING A THERMISTOR POSITIONABLE CONTIGUOUS TO SAID COOLING MEANS, SAID THERMISTOR HAVING AN ELECTRICAL RESISTANCE WHICH VARIES AS A FUNCTION OF THE TEMPERATURE THEREOF, AN ELECTRICAL RESISTANCE NETWORK INCLUDING SAID THERMISTOR, AND AN ELECTRICAL CIRCUIT INCLUDING AN ELECTRONIC TRANSDUCER AND MEANS FOR CONTROLLING THE CONDUCTIVITY OF SAID TRANSDUCER AS A FUNCTION OF THE RESISTANCE OF SAID THERMISTOR, SAID TRANSDUCER BEING INTERCONNECTABLE WITH SAID DEFROST MEANS FOR ENERGIZING SAID DEFROST MEANS WHEN THE TEMPERATURE OF SAID THERMISTOR IS DEPRESSED BELOW A FIRST PRESELECTED TEMPERATURE LEVEL, SAID NETWORK INCLUDING MEANS FOR MODIFYING THE RESISTANCE THEREOF SUBSTANTIALLY CONCURRENTLY WITH THE ENERGIZATION OF THE DEFROST MEANS AND WHILE THE DEFROST MEANS IS ENERGIZED THEREBY TO PROVIDE A SUBSTANTIAL DIFFERENTIAL IN THE OPERATION OF SAID CIRCUIT, WHEREBY AS THE FROST ON SAID COOLING MEANS BUILDS UP AND ENVELOPS SAID THERMISTOR THE TEMPERATURE THEREOF IS DEPRESSED BELOW SAID FIRST PRESELECTED LEVEL AND SAID DEFROST MEANS IS ENERGIZED, AND WHEREBY SAID DEFROST MEANS IS THEREAFTER DEENERGIZED ONLY AFTER THE TEMPERATURE OF SAID THERMISTOR RISES ABOVE A SECOND PRESELECTED TEMPERATURE SUBSTANTIALLY HIGHER THAN SAID FIRST PRESELECTED TEMPERATURE.