Patent GB-958483-A (GB)
Title: Refrigerator
IPC: F25D21/00
Filed: 1963-04-11
Abstract: 958,483. Refrigerators; defrosting. GENERAL MOTORS CORPORATION. April 11, 1963 [April 30, 1962], No. 14703/63. Heading F4H. In a refrigerator having a freezer compartment and a storage compartment between which air is circulated, a thermo-responsive defrost control device is arranged to be subject to the evaporator temperature, the temperature of the air passing from the storage compartment, the flow of this air being subject to frost accumulation on the evaporator, and the temperature of an electric heater. As shown in Figs. 1 and 3, the refrigerator comprises a storage compartment 32, a freezer compartment 30, a finned evaporator 42 beneath a false bottom wall 40 in the freezer compartment and a fan 90 at the rear of the latter compartment. Air from the storage compartment is drawn through passages 64 above the top wall 54 of that compartment and forwardly over the sides of the evaporator before being drawn rearwardly over the central portion of the evaporator to the inlet of fan 90 together with an air stream drawn from the freezer compartment through apertures 84. The fan 90 discharges through an outlet 96 to the freezer compartment and through passages 121, 123, 125 and 137 under the control of a valve 149 to the storage compartment. A container 250 is mounted on the evaporator at the point thereof which is first contacted by air from the storage compartment (see Fig. 3). The container 250 houses a bimetallic switch 187 and has an electric heater 274 secured thereto (Figs. 5 and 7), the switch 187 being movable between a contact 185, in which position it energizes the compressor motor 167 and the fan motor 94, and a contact 254, in which position it energizes an electric defrost heater 260. When the switch 187 abuts contact 185 the compressor and fan motors are cycled by a switch 181 controlled by a temperature sensitive element 222 responsive to the temperature of the freezing compartment. In the embodiment of Fig. 5 the heater 274 is in series with a resistance 266 and a switch 238 which is operated by a projection 155 on the stem 147 of valve 149 (see Fig. 1). The resistance 266 has a negative temperature coefficient and is mounted in a capsule 267 (Fig. 1) on the rear of the refrigerator cabinet so as to be responsive to ambient air temperature. During normal operation the heat from the warm air from the storage compartment contacting the container 250 and the heat from the heater 274 is sufficient to maintain switch 187 against contact 185, but when frost accumulates on the evaporator and container 250 the flow of warm air over the latter is reduced. Thus, when the switch 238 opens due to valve 149 reaching its wide-open position, the switch 187 cools and moves to contact 254 to initiate defrosting. In low ambient temperature conditions the switch 238 remains closed since compartment 32 is sufficiently cold and valve 149 does not open sufficiently but the resistance 266 decreases the current to the heater 274 enabling the switch 187 to cool and initiate defrosting as before. In another embodiment (Fig. 6, not shown), the resistance 266 is omitted and a resistance having a positive temperature coefficient is connected in parallel with the switch 238, so that at low ambient temperatures a short defrost period occurs and vice versa. In Fig. 7, the switch 238 is omitted and a resistance 359 having a positive temperature coefficient is connected in series and a resistance 351 having a negative temperature coefficient in parallel with the heater, the resistances 351 and 359 combining to reduce the current to the heater as the ambient temperature rises. In a final embodiment (Fig. 8, not shown), the valve-operated switch 238 is connected in series with the resistance 351 of Fig. 7 and the resistance 359 is omitted so that the heater is by-passed and switch 187 operated when the switch 238 is closed. The resistance 351 delays operation of the switch 187 more in low ambient temperatures than in high. The switch 187 may be adapted to operate a reversing valve, to initiate hot gas defrosting, rather than the heater 260.