Patent ID: 7448226

Claim:
A refrigerator system using a hydrocarbon-based cooling medium, the system comprising: a compressor, a condenser, and at least one evaporator operatively coupled together and containing the hydrocarbon-based cooling medium and a machine oil therein; a cooling fan arranged to cool said compressor; and a controller configured to: operate said compressor at an operational speed; control an ON/OFF state of said cooling fan; evaluate an air temperature of an environment in which the refrigerator system is arranged and, responsive to a determination that the air temperature is less than a first temperature, stop the cooling fan; and responsive to a determination that the air temperature is equal to or greater than the first temperature and that a temperature difference between an inlet and an outlet of said at least one evaporator is less than a predetermined value, start said cooling fan, wherein said control of the ON/OFF state of said cooling fan operates to heat the hydrocarbon-based cooling medium at least to a temperature that reduces an amount of the hydrocarbon-based cooling medium dissolved in the machine oil at least to a level that reduces a sleeping phenomenon of the hydrocarbon-based cooling medium.