Refrigerator-freezer controller of refrigenator-freezer, and method for determination of leakage of refrigerant

• US 20050086952A1
• Filed: 09/19/2002
• Published: 04/28/2005
• Est. Priority Date: 09/19/2001
• Status: Abandoned Application

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Hashimoto, Shoji, Yamamoto, Ryousuke, Hirai, Shinji, Saruta, Susumu, Uenoyama, Yoshihiko, Nonaka, Hikaru, Sumihiro, Katsushi, Sakuma, Tsutomu, Horie, Munehiro
• Application Number:
  US10/490,123
• Publication Number:
  US 20050086952A1
• Time in Patent Office: Days
• US Class Current: 62/129
• CPC Class Codes: F25B 2400/12 Inflammable refrigerants
• CPC Class Codes: F25B 2500/222 Detecting refrigerant leaks
• CPC Class Codes: F25B 2600/0251 with on-off operation
• CPC Class Codes: F25B 2600/0253 with variable speed
• CPC Class Codes: F25B 2600/2507 Flow-diverting valves
• CPC Class Codes: F25B 2700/171 of the compressor
• CPC Class Codes: F25B 2700/21174 of the refrigerant at the inlet of the evaporator
• CPC Class Codes: F25B 2700/21175 of the refrigerant at the outlet of the evaporator
• CPC Class Codes: F25B 49/005 of safety devices F25B49/02 and F25B49/04 take precedence
• CPC Class Codes: F25B 5/02 arranged in parallel
• CPC Class Codes: F25D 11/022 with two or more evaporators
• CPC Class Codes: F25D 17/065 with compartments at different temperatures
• CPC Class Codes: F25D 2317/0682 Two or more fans
• CPC Class Codes: F25D 2400/04 Refrigerators with a horizontal mullion
• CPC Class Codes: F25D 2700/10 Sensors measuring the temperature of the evaporator
• CPC Class Codes: F25D 2700/12 Sensors measuring the inside temperature
• CPC Class Codes: F25D 2700/122 of freezer compartments
• CPC Class Codes: F25D 2700/14 Sensors measuring the temperature outside the refrigerator or freezer
• CPC Class Codes: F25D 29/00 Arrangement or mounting of control or safety devices
• CPC Class Codes: Y02B 30/70 Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating
• CPC Class Codes: Y02B 40/00 : Technologies aiming at improving the efficiency of home appliances, e.g. induction cooking or efficient technologies for refrigerators, freezers or dish washers

Abstract

A refrigerator-freezer is described, in which refrigerant leakage from the refrigeration cycle can be safely detected. The refrigerator-freezer comprises: a refrigeration cycle formed by a compressor, a capillary, an evaporator and an accumulator connected in series, and filled with a flammable refrigerant; a cooling fan configured to blow the cold air cooled by the evaporator in the refrigerator-freezer; and a refrigerant leakage detection system configured to detect leakage of the flammable refrigerant, wherein the refrigerant leakage detection system is provided with a temperature sensor configured to measure the temperature of a refrigerant conduit of the evaporator and judges that the flammable refrigerant is leaking in the low pressure side of the refrigeration cycle when the temperature is detected by the temperature sensor with the compressor being halted is no lower than a predetermined temperature.

Claims

1. A refrigerator-freezer comprising:

a refrigeration cycle formed by a compressor, a capillary, an evaporator and an accumulator connected in series, and filled with a flammable refrigerant;

a cooling fan configured to blow the cold air cooled by said evaporator in said refrigerator-freezer; and

a refrigerant leakage detection system configured to detect leakage of said flammable refrigerant,

wherein said refrigerant leakage detection system is provided with a temperature sensor configured to measure the temperature of a refrigerant conduit of said evaporator and judges that said flammable refrigerant is leaking in the low pressure side of the refrigeration cycle when the temperature is detected by said temperature sensor with said compressor being halted is no lower than a predetermined temperature.

7. A refrigerator-freezer comprising:

a refrigeration cycle formed by a compressor, a capillary, an evaporator and an accumulator connected in series, and filled with a flammable refrigerant;

a cooling fan configured to blow the cold air cooled by said evaporator in said refrigerator-freezer; and

a refrigerant leakage detection system configured to detect leakage of said flammable refrigerant,

wherein said refrigerant leakage detection system is provided with a temperature sensor configured to measure the temperature of a refrigerant conduit of said evaporator and judges that said flammable refrigerant is leaking from the high pressure side of the refrigeration cycle when the temperature detected by said temperature sensor with said compressor being operated is no higher than a predetermined temperature.

2. The refrigerator-freezer as claimed in claim 7 wherein said refrigerant conduit is a refrigerant conduit located in the inlet port side of said evaporator.

3. The refrigerator-freezer as claimed in claim 7 wherein, when it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking, the operation of said compressor is halted.

4. The refrigerator-freezer as claimed in claim 7 wherein, when it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking, a notice such as an alarm is generated a predetermined time after the detection of refrigerant leakage.

5. The refrigerator-freezer as claimed in claim 7 wherein a ventilation conduit for intercommunicating with the external space is provided in the bottom section of a cooling room in which is located the evaporator and wherein, when it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking, the operation of said cooling fan is halted.

6. The refrigerator-freezer as claimed in claim 7 wherein when the operation of said compressor is continued without a halt, said compressor is halted for every predetermined time period.

8. The refrigerator-freezer as claimed in claim 7 wherein said refrigerant conduit is a refrigerant conduit located in the inlet port side of said evaporator.

9. The refrigerator-freezer as claimed in claim 7 wherein a ventilation conduit for intercommunicating with the external space is provided in the bottom section of a cooling room in which is located the evaporator and wherein, when it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking, the operation of said cooling fan is halted.

10. The refrigerator-freezer as claimed in claim 7 wherein, when it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking, the operation of said compressor is halted.

11. The refrigerator-freezer as claimed in claim 7 wherein, when it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking, a notice such as an alarm is generated a predetermined time after the detection of refrigerant leakage.

12. The refrigerator-freezer as claimed in claim 7 wherein when the operation of said compressor is continued without a halt, said compressor is halted for every predetermined time period.

13. A refrigerator-freezer comprising:

a refrigeration cycle formed by a compressor, a capillary, an evaporator and an accumulator connected in series, and filled with a flammable refrigerant;

a cooling fan configured to blow the cold air cooled by said evaporator in said refrigerator-freezer; and

a refrigerant leakage detection system configured to detect leakage of said flammable refrigerant,

wherein said refrigerant leakage detection system is provided with a temperature sensor configured to measure the temperature of a refrigerant conduit of said evaporator and judges that said flammable refrigerant is leaking in the high pressure side of the refrigeration cycle when the temperature detected by said temperature sensor is no lower than a predetermined temperature while the input power to said compressor is decreasing, and that said flammable refrigerant is leaking in the low pressure side of the refrigeration cycle when the temperature detected by said temperature sensor is no higher than a predetermined temperature while the input power to said compressor is increasing.

14. The refrigerator-freezer as claimed in claim 13 wherein a ventilation conduit for intercommunicating with the external space is provided in the bottom section of a cooling room in which is located the evaporator and wherein, when it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking, the operation of said cooling fan is halted.

15. A refrigerator-freezer comprising:

a refrigeration cycle formed by a compressor, a capillary, an evaporator and an accumulator connected in series, and filled with a flammable refrigerant;

a cooling fan configured to blow the cold air cooled by said evaporator in said refrigerator-freezer; and

a refrigerant leakage detection system configured to detect leakage of said flammable refrigerant,

wherein said refrigerant leakage detection system is provided with temperature sensors configured to measure the temperatures of refrigerant conduits in the inlet and outlet port sides of said evaporator and judges that said flammable refrigerant is leaking in the high pressure side of the refrigeration cycle when the differential temperature between temperatures detected by said temperature sensors is no lower than a predetermined temperature while the input power to said compressor is decreasing, and that said flammable refrigerant is leaking in the low pressure side of the refrigeration cycle when the differential temperature between temperatures detected by said temperature sensors is no higher than a predetermined temperature while the input power to said compressor is increasing.

16. The refrigerator-freezer as claimed in claim 15 wherein a temperature sensor is provided on or near the accumulator to measure the temperature of the conduit in the outlet port side of said evaporator and functions also as a temperature sensor for detecting the timing of starting a defrosting operation.

17. The refrigerator-freezer as claimed in claim 15 wherein a ventilation conduit for intercommunicating with the external space is provided in the bottom section of a cooling room in which is located the evaporator and wherein, when it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking, the operation of said cooling fan is halted.

18. The refrigerator-freezer as claimed in claim 15 wherein, when it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking, the operation of said compressor is halted.

19. The refrigerator-freezer as claimed in claim 15 wherein, when it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking, a notice such as an alarm is generated a predetermined time after the detection of refrigerant leakage.

20. A refrigerator-freezer comprising:

a refrigeration cycle formed by a compressor, a capillary, an evaporator and an accumulator connected in series, and filled with a flammable refrigerant;

a cooling fan configured to blow the cold air cooled by said evaporator in said refrigerator-freezer; and

a temperature sensor configured to measure the temperature of said flammable refrigerant flowing in said evaporator; and

a refrigerant leakage detection system configured to monitor the temperature change of said flammable refrigerant by said temperature sensor and judge leakage of said flammable refrigerant on the basis of the temperature change with reference to the state transitions of said refrigerator-freezer.

21. The refrigerator-freezer as claimed in claim 20 wherein the refrigerator-freezer is provided with a refrigerant confinement mechanism configured to confine said flammable refrigerant in a location of the refrigerant conduit from which said flammable refrigerant does not leak into a freezer compartment and a fresh-food compartment of said refrigerator-freezer when it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking.

22. The refrigerator-freezer as claimed in claim 20 wherein, when it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking, a notice such as an alarm is generated.

23. The refrigerator-freezer as claimed in claim 20 wherein, when it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking, the operation of said compressor is halted.

25. The refrigerator-freezer as claimed in claim 20 wherein the refrigerator-freezer is provided with a refrigerant confinement mechanism configured to confine said flammable refrigerant in a location of the refrigerant conduit from which said flammable refrigerant does not leak into the freezer compartment and the fresh-food compartment of said refrigerator-freezer when it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking.

29. The refrigerator-freezer as claimed in claim 25 wherein, when it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking, said refrigerant confinement mechanism serves to confine said flammable refrigerant in a high pressure location between the refrigerant draining side of said compressor and a check valve by closing said check valve and driving said compressor for a predetermined time period.

24. A refrigerator-freezer comprising:

a thermal insulated cabinet in which a fresh-food compartment and a freezer compartment are defined;

a fresh-food compartment evaporator configured to cool said fresh-food compartment;

a fresh-food compartment capillary located in the inlet port side of said fresh-food compartment evaporator;

a freezer compartment evaporator configured to cool said freezer compartment;

a freezer compartment capillary located in the inlet port side of said freezer compartment evaporator;

a refrigerant path switch mechanism located in the upstream side of said fresh-food compartment capillary and said freezer compartment capillary and configured to switch the refrigerant path for selectively supplying said flammable refrigerant to said fresh-food compartment evaporator and said freezer compartment evaporator;

a compressor constituting a circulation path of said flammable refrigerant including two routes for cooling said fresh-food compartment and said freezer compartment as a cooling cycle of said refrigerator-freezer together with said fresh-food compartment evaporator, said freezer compartment evaporator, said fresh-food compartment capillary, said freezer compartment capillary and said refrigerant path switch mechanism and configured to compress said flammable refrigerant;

a temperature sensor located configured to detect the temperature of said flammable refrigerant flowing in at least one of said fresh-food compartment evaporator and said freezer compartment evaporator; and

a refrigerant leakage detection system configured to monitor the temperature change of said flammable refrigerant by said temperature sensor and judge leakage of said flammable refrigerant on the basis of the temperature change with reference to the state transitions of said refrigerator-freezer.

26. The refrigerator-freezer as claimed in claim 24 wherein, when it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking, a notice such as an alarm is generated.

27. The refrigerator-freezer as claimed in claim 24 wherein, when it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking, the operation of an electric device preselected of said refrigerator-freezer is halted.

28. The refrigerator-freezer as claimed in claim 24 wherein, when it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking, said refrigerant confinement mechanism serves to confine said flammable refrigerant in a high pressure location between the refrigerant draining side of said compressor and said refrigerant path switch mechanism by closing said refrigerant path switch mechanism and driving said compressor for a predetermined time period.

30. The refrigerator-freezer as claimed in claim 24 wherein said temperature sensor is provided in each of the inlet port side and the outlet port side of said freezer compartment evaporator or said fresh-food compartment evaporator and

wherein when the differential temperature of said flammable refrigerant between the inlet port side and the outlet port side exceeds a predetermined value, it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking.

31. The refrigerator-freezer as claimed in claim 24 wherein said temperature sensor is provided in each of the inlet port side and the outlet port side of said freezer compartment evaporator or said fresh-food compartment evaporator and

wherein when the differential temperature of said flammable refrigerant between the inlet port side and the outlet port side continuously exceeds a predetermined value for a predetermined time period, it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking.

32. The refrigerator-freezer as claimed in claim 24 wherein said temperature sensor is provided in each of the inlet port side and the outlet port side of said fresh-food compartment evaporator and

wherein when the differential temperature of said flammable refrigerant between the inlet port side and the outlet port side continuously exceeds 10 K for 5 minutes, it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking.

33. The refrigerator-freezer as claimed in claim 24 wherein said temperature sensor is provided in each of the inlet port side and the outlet port side of said freezer compartment evaporator and

wherein when the differential temperature of said flammable refrigerant between the inlet port side and the outlet port side continuously exceeds 5 K for 5 minutes, it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking.

34. The refrigerator-freezer as claimed in claim 33 wherein, in a freezer compartment cooling mode just after starting the operation of said compressor, said refrigerant leakage detection system judges whether or not said flammable refrigerant is leaking on the basis of the temperature as detected by said temperature sensor a predetermined time after starting the freezer compartment cooling mode.

35. The refrigerator-freezer as claimed in claim 24 wherein said temperature sensor is provided in the inlet port side of said freezer compartment evaporator or said fresh-food compartment evaporator and

wherein said refrigerant leakage detection system serves to store the temperature data as detected by said temperature sensor and judges that said flammable refrigerant is leaking when the current temperature of said flammable refrigerant is no higher than the average temperature in the previous cycle minus a predetermined value.

36. The refrigerator-freezer as claimed in claim 24 wherein said temperature sensor is provided in the inlet port side of said freezer compartment evaporator or said fresh-food compartment evaporator and

wherein said refrigerant leakage detection system serves to store the temperature data as detected by said temperature sensor and judges that said flammable refrigerant is leaking when the current temperature of said flammable refrigerant is continuously no higher than the average temperature in the previous cycle minus a predetermined value for a predetermined time period.

37. The refrigerator-freezer as claimed in claim 36 wherein when the current temperature of said flammable refrigerant is continuously lower than the average temperature by no lower than 5 K for 20 minutes, it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking.

38. The refrigerator-freezer as claimed in claim 36 wherein said flammable refrigerant is a hydrocarbon base flammable refrigerant (HC refrigerant).

39. A control device for a refrigerator-freezer comprising:

a thermal insulated cabinet in which a fresh-food compartment and a freezer compartment are defined;

a fresh-food compartment evaporator configured to cool said fresh-food compartment;

a fresh-food compartment capillary located in the inlet port side of said fresh-food compartment evaporator;

a freezer compartment evaporator configured to cool said freezer compartment;

a freezer compartment capillary located in the inlet port side of said freezer compartment evaporator;

a refrigerant path switch mechanism located in the upstream side of said fresh-food compartment capillary and said freezer compartment capillary and configured to switch the refrigerant path for selectively supplying said flammable refrigerant to said fresh-food compartment evaporator and said freezer compartment evaporator;

a compressor constituting a circulation path of said flammable refrigerant including two routes for cooling said fresh-food compartment and said freezer compartment as a cooling cycle of said refrigerator-freezer together with said fresh-food compartment evaporator, said freezer compartment evaporator, said fresh-food compartment capillary, said freezer compartment capillary and said refrigerant path switch mechanism and configured to compress said flammable refrigerant;

a controller configured to calculate the frequency of said compressor on the basis of a PID calculation with reference to the inner temperatures of said fresh-food compartment and said freezer compartment, and control said compressor and said refrigerant path switch mechanism in accordance with the frequency as calculated in order to alternately cool said fresh-food compartment and said freezer compartment,

wherein said control device is provided with a refrigerant leakage detection system configured to judge refrigerant leakage on the basis of the rate of change of the duty ratio of said compressor.

40. The control device for the refrigerator-freezer as claimed in claim 39 wherein the rate of change of the duty ratio is the rate of change of the average duty ratio in the current cycle of a cooling mode relative to the average duty ratio in the previous cycle of the same cooling mode.

41. The control device for the refrigerator-freezer as claimed in claim 39 wherein the rate of change of the duty ratio is the rate of change of the duty ratio in the current cycle of a cooling mode relative to a base duty ratio at a predetermined time point in a past cycle of the same cooling mode.

42. The control device for the refrigerator-freezer as claimed in claim 41 wherein said base duty ratio is the rate duty ratio at a time point when the refrigerant path is switched by means of said refrigerant path switch mechanism.

43. The control device for the refrigerator-freezer as claimed in claim 41 wherein said base duty ratio is the duty ratio at a time point when the frequency of the compressor is changed in the previous cycle.

44. The control device for the refrigerator-freezer as claimed in claim 39 wherein said refrigerant leakage detection system judges that said flammable refrigerant is leaking in the high pressure side of the refrigeration cycle when the decrease of the duty ratio is no smaller than a predetermined value.

45. The control device for the refrigerator-freezer as claimed in claim 39 wherein said refrigerant leakage detection system judges that said flammable refrigerant is leaking in the high pressure side of the refrigeration cycle when the increase of the duty ratio is no smaller than a predetermined value.

46. The control device for the refrigerator-freezer as claimed in claim 39 wherein a temperature sensor is provided in each of the inlet port and the outlet port of said freezer compartment evaporator, and

wherein when the differential temperature of said flammable refrigerant between the inlet port side and the outlet port side of said freezer compartment evaporator exceeds a predetermined value while the increase of the current duty ratio exceeds a predetermined value, it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking in the low pressure side of the refrigeration cycle.

47. The control device for the refrigerator-freezer as claimed in claim 39 wherein when the decrease of the duty ratio exceeds a predetermined value while the increase of the frequency as calculated on the basis of the PID calculation exceeds a predetermined value, it is judged by said refrigerant leakage detection system that said flammable refrigerant is leaking in the high pressure side of the refrigeration cycle.

48. A method of judging refrigerant leakage for a refrigerator-freezer comprising:

a thermal insulated cabinet in which a fresh-food compartment and a freezer compartment are defined;

a fresh-food compartment evaporator configured to cool said fresh-food compartment;

a fresh-food compartment capillary located in the inlet port side of said fresh-food compartment evaporator;

a freezer compartment evaporator configured to cool said freezer compartment;

a freezer compartment capillary located in the inlet port side of said freezer compartment evaporator;

a refrigerant path switch mechanism located in the upstream side of said fresh-food compartment capillary and said freezer compartment capillary and configured to switch the refrigerant path for selectively supplying said flammable refrigerant to said fresh-food compartment evaporator and said freezer compartment evaporator;

a compressor constituting a circulation path of said flammable refrigerant including two routes for cooling said fresh-food compartment and said freezer compartment as a cooling cycle of said refrigerator-freezer together with said fresh-food compartment evaporator, said freezer compartment evaporator, said fresh-food compartment capillary, said freezer compartment capillary and said refrigerant path switch mechanism and configured to compress said flammable refrigerant;

a controller configured to calculate the frequency of said compressor on the basis of a PID calculation with reference to the inner temperatures of said fresh-food compartment and said freezer compartment, and control said compressor and said refrigerant path switch mechanism in accordance with the frequency as calculated in order to alternately cool said fresh-food compartment and said freezer compartment,

wherein refrigerant leakage is judged by comparing the duty ratio in the current cycle of a cooling mode with the duty ratio in the previous cycle of the same cooling mode.

49. The method of judging refrigerant leakage for the refrigerator-freezer as claimed in claim 48 wherein refrigerant leakage is judged by comparing the duty ratio in the current cycle of the cooling mode in a predetermined timing with the duty ratio in the previous cycle of the same cooling mode in the same timing.

50. The method of judging refrigerant leakage for the refrigerator-freezer as claimed in claim 48 wherein the duty ratios are compared with each other at the same frequency of the compressor.

51. The method of judging refrigerant leakage for the refrigerator-freezer as claimed in claim 48 wherein when the decrease of the duty ratio as a result of the comparison in the duty ratio of said compressor exceeds a predetermined value, it is judged that said flammable refrigerant is leaking in the high pressure side.

52. The method of judging refrigerant leakage for the refrigerator-freezer as claimed in claim 48 wherein when the increase of the duty ratio as a result of the comparison in the duty ratio of said compressor exceeds a predetermined value, it is judged that said flammable refrigerant is leaking in the low pressure side.

53. The method of judging refrigerant leakage for the refrigerator-freezer as claimed in claim 48 wherein when the decrease of the duty ratio as a result of the comparison in the duty ratio of said compressor exceeds a predetermined value or when the increase of the duty ratio as a result of the comparison in the duty ratio of said compressor exceeds a predetermined value, said refrigerant path switch mechanism and the frequency of said compressor are fixed for a predetermined period.

54. A method of judging refrigerant leakage for a refrigerator-freezer comprising:

a thermal insulated cabinet in which a fresh-food compartment and a freezer compartment are defined;

a fresh-food compartment evaporator configured to cool said fresh-food compartment;

a fresh-food compartment capillary located in the inlet port side of said fresh-food compartment evaporator;

a freezer compartment evaporator configured to cool said freezer compartment;

a freezer compartment capillary located in the inlet port side of said freezer compartment evaporator;

a refrigerant path switch mechanism located in the upstream side of said fresh-food compartment capillary and said freezer compartment capillary and configured to switch the refrigerant path for selectively supplying said flammable refrigerant to said fresh-food compartment evaporator and said freezer compartment evaporator;

a compressor constituting a circulation path of said flammable refrigerant including two routes for cooling said fresh-food compartment and said freezer compartment as a cooling cycle of said refrigerator-freezer together with said fresh-food compartment evaporator, said freezer compartment evaporator, said fresh-food compartment capillary, said freezer compartment capillary and said refrigerant path switch mechanism and configured to compress said flammable refrigerant;

a controller configured to calculate the frequency of said compressor on the basis of a PID calculation with reference to the inner temperatures of said fresh-food compartment and said freezer compartment, and control said compressor and said refrigerant path switch mechanism in accordance with the frequency as calculated in order to alternately cool said fresh-food compartment and said freezer compartment,

wherein, while the duty ratio in the current cycle of a cooling mode is compared with the duty ratio in the previous cycle of the same cooling mode and the differential temperature between the inlet port and the outlet port of the freezer compartment evaporator is measured,

it is judged that said flammable refrigerant is leaking in the low pressure side of the refrigeration cycle when the differential temperature of said flammable refrigerant between the inlet port side and the outlet port side of said freezer compartment evaporator exceeds a predetermined value while the increase of the current duty ratio exceeds a predetermined value.