GB784509A - Improvements in or relating to electrically operated compression refrigeration apparatus - Google Patents

Abstract

784,509. Refrigerating. HERON, A. G. April 22, 1955 [March 4, 1954], No. 6329/54. Class 29 Defrosting a refrigerator evaporator by an electric heater DH is initiated by a timer T and is controlled by a switch P responsive to pressure in the evaporator and a thermostat ES responsive to the evaporator temperature. In Fig. 1, a circuit embodying a two pole time switch T is shown in which the compression motor circuit including a compression motor CM, a pressure switch LP, to safeguard against any faults in refrigerant circulation, and a thermostat CS, all in series, and the heater circuit including heater DH, pressure switch P and thermostat ES, all in series, are connected in parallel across the mains to poles 3 and 2 respectively of the switch T. In normal operation the switch is set at 3 and cycling of the compressor according to the temperature of the cold room is carried on. At a predetermined time the time switch sets at 2 and defrosting is initiated when the pressure inside the evaporator exceeds a certain limit the pressure switch P opens, the heater is cut off and the pressure allowed to drop until P closes again. The cycle continues until the timer switches back to position 3. Further control is obtained by the thermostat ES which opens when the temperature of the evaporator exceeds a certain value and cause defrosting to cease; this may be signalled by a lamp L indicating the necessity of manual resetting of the thermostat. An alternative arrangement utilizing a single pole switch is shown in Fig. 2, where closure of the time switch ST causes a solenoid operated switch 7, 8 normally closed, to cut in the heater circuit and cut out the compressor motor circuit. Reference has been directed by the Comptroller to Specification 694,763.