Patent GB-747160-A (GB)
Title: Improvements relating to refrigerator control systems
IPC: F25D21/00
Filed: 1954-06-25
Abstract: 747,160. Thermal switches; actuation of switches. GENERAL ELECTRIC CO. June 25, 1954 [June 30, 1953], No. 18728/54. Class 38(5) [Also in Group XIII] An automatic defrosting system is provided for a thermostatically-controlled refrigerator wherein de-frosting by heating is initiated in response to the time in which the door is open while the compressor motor is running. The end of the defrosting period occurs when the refrigerator is raised to a particular temperature. The initially warm refrigerator contains a sensing tube 4, the expansion of the fluid therein causing bellows 3 to push upward a rod 5 against the action of an adjustable spring 9. A lever 11, pivoted at one end at 12 and having its other end engaging the end 16 of a non-centre hairpin toggle spring 15 having its other end 17 engaging a stationary part of the device; has a knife edge connection 14 with a. rod 5. When the rod 5 moves upward, extension 13 of lever 11 closes the contacts 21 and 22. If the contacts 65, 69 arranged on flexible. members 57 and 67 are also closed, the compressor motor 23 will operate, power being supplied through lines 33 and 29. The opening of the refrigerator door 42 closes the contacts 40, 45 and 43, 45, the latter causing a lamp 44 inside the refrigerator to light up, the former energizing a synchronous timing motor 35 which drives, through gearing, a cam 51. A cam follower 55 is seated in a slot in an intermediate flexible member 67 placed between members 58, 57. When the end of the cam follower 55 falls off the high point 52 to the low point 53 of the cam 51, under the influence of the flexible member 67 tending to the right, the circuits of the timing motor 35 and the compressor motor 23 are opened, contacts 65 and 69 being broken but contacts 70 and 66 carried by flexible members 58, 67 close. The closure of contacts 70, 66 causes the flow of current through the heater 47 for de-frosting. When the temperature of the refrigerator has risen sufficiently, rod 5 will push upward a' screw 84 seated in a leaf spring tripping lever 78 secured at 80. Said lever 78, biased by its bent section 83 into contact at its end 81 with a spacing member 63 of the flexible members, is caused to rise off its stop 82 to break its contact with member 63. Since the flexible members tend to move to the right, members 58 and 57 will now do so, member 58 being movable in a slot in the cam follower 55. Member 67 however, because the follower 55 is in contact with the low point 53 of the cam 51, remains stationary and the contacts 70, 66 are opened and contacts 65, 69 closed. Operation of the motor 23 will ensue, together with the rotation of the cam 51 if the door is open. The cam follower pushes the flexible member assembly to the left as it follows the cam and, as the refrigerator cools, the end 81 of tripping lever 78 again makes contact with spacing member 63 to set the system in its initial condition. If the door is closed when the'contacts 65, 69 are closed, in the subsequent cooling, lever 78 will rest on the top of the spacing member 63 until the door is opened when the rotation of cam 51 will allow it to fall to its initial position resting on the stop 82. Specifications 738,497 and 740,523 are referred to.