Patent GB-948223-A (GB)
Title: Refrigerator
IPC: F25D17/06
Filed: 1962-03-30
Abstract: 948,223. Refrigerators; defrosting. GENERAL MOTORS CORPORATION. March 30, 1962 [April 24, 1961; May 29, 1961], No. 12282/62. Heading F4H. In a refrigerator as described in Specification 948,224 when the compressor motor is deenergized and when the storage compartment temperature rises to a predetermined value, the air fan motor is de-energized and a heater is energized to defrost the evaporator. As shown in Fig. 4, the motor 147 of the compressor 145 is connected between supply leads 169 and 155 in series with a fixed contact 157 of a double throw switch 159 which is operated by a fluid motor 161 having a capillary tube 163. The latter includes portions 164 and 166 which are respectively in contact with the liner 38 of the freezer compartment and with the air leaving the storage compartment 32. The other fixed contact 171 is connected to a circuit 191 containing a switch 179 mounted on the rear wall of the storage compartment and a defrost limit switch 175, and a parallel circuit 195 containing a high resistance heater 193 which is wrapped around the portion 164 of the capillary tube 163, the circuits being connected to one end of a defrost heater 177 mounted on the evaporator fins. During normal operating conditions switch 179 is open and switch 175 closed and the switch 159 energizes the compressor motor when the temperature of the air leaving the storage compartment reaches 11‹ F. as sensed by the capillary portion 166 and de-energizes it when the temperature of the liner 38 drops to - 2‹ F. as sensed by portion 164. During idle periods the heater 193 warms the portion 164 to counteract the cooling effect of the liner and to prevent this portion from exercising control over the switch 159 during such periods. The fan motor 92 which is connected between supply lead 169 and the switch 175 is energized continuously during normal operation. When frost builds up on the evaporator the temperature of air supplied to the storage compartment rises and the switch 179, which includes a bimetallic arm 181, closes so that when the movable contact 167 of switch 159 moves to fixed contact 171 the compressor motor is de-energized, the defrost heater 177 is energized and the heater 193 and fan motor 92 are short circuited. The defrost limit switch 175 opens when the temperature of the evaporator reaches 50‹ F., thus de-energizing heater 177 and energizing heater 193 so that the capillary tube portion 166 operates switch 159 to restart the compressor, The fan motor remains inoperative until the switch 175 closes at an evaporator temperature of 22 ‹ F. In an alternative embodiment, the control circuit (Fig. 6) includes a switch 232 controlled by the movement of the valve admitting air to the storage compartment. The circuit also includes a double throw switch having an operating coil 199 and a movable contact 198 which is normally in contact with a fixed contact 196 so that the fan motor 92 is energized continuously and the compressor motor energized under the control of a switch 202 controlled by a fluid motor 161 as before. When defrosting is required the movable contact 238 of switch 232 is moved to contact 242 so that when switch 202 opens, the coil 199 is energized and moves contact 198 to contact 254, thus energizing the defrost heater 177. The defrost limit switch 175 terminates defrosting as before.