Defrost control system for a refrigerator

A modular control system for a vending machine having a refrigerated compartment, a compressor, an evaporator, and an evaporator heater, the modular control system, comprising:

• A. a compartment temperature sensor within the refrigerated compartment:
• B. an evaporator temperature sensor on the evaporator;
• C. a controller, electrically coupled to the compartment temperature sensor. wherein the controller produces a compressor activation signal which activates the compressor in response to the temperature of the compartment temperature sensor rising above a certain specified range and a compressor deactivation signal which deactivates the compressor in response to the temperature of the compartment temperature sensor falling below the certain specified temperature range,
• D. a timing means for generating a defrost cycle time signal;
• E. a timing means for generating a maximum heating time signal:
• F. the controller, responsive to the defrost cycle time signal, producing a start defrost control signal which activates the heater and deactivates the compressor:
• G. the controller, electrically coupled to the evaporator temperature sensor, producing a stop defrost control signal which deactivates the heater and activates the compressor in response to the temperature of the evaporator temperature sensor rising above a specified evaporator temperature, or in response to the maximum heating time signal;
• wherein the controller includes a communication means for communicating the certain specified temperature range, the temperature of the evaporator temperature sensor and the temperature of the compartment temperature sensor to a second controller on the vending machine, wherein said second controller can display said certain specified temperature range, and the temperatures of the evaporator temperature sensor and compartment temperature sensor by communicating with the controller through said communication means.

A method of controlling and defrosting a refrigerated product dispenser cabinet, including a compressor and an evaporator heater, comprising the steps of:

• A. receiving and storing a maximum cabinet temperature value, a minimum cabinet temperature value, a defrost cycle time value, a heated defrost time-out value and a maximum evaporator temperature value;
• B. sensing the temperature within the cabinet and the temperature of the evaporator;
• C. cyclically monitoring the cabinet temperature and activating the compressor when the cabinet temperature is above the maximum cabinet temperature value and deactivating the compressor when the cabinet temperature is below the minimum cabinet temperature;
• D. advancing and monitoring a system timer;
• E. activating the heater when the defrost cycle time value is reached by the timer and deactivating the heater when the heated defrost time-out value is reached by the timer or the cabinet temperature has reached the maximum cabinet temperature value, and
• F. activating the compressor.