GB1023520A - De-ice control - Google Patents

Abstract

1,023,520. Defrosting. RANCO Inc. Dec. 9, 1964 [Dec. 11, 1963], No. 50170/64. Heading F4H. A defrosting control comprises an arm movable between defrosting initiation and termination positions, a thermal element adapted to control the movement of said arm and a timer which prevents movement of said arm to its initiation position except at given intervals. As shown, a flexible switch arm 51 carries a contact 50 for snap-acting movement between fixed contacts 49, 50, the arm 51 being actuated by an arm 55 which is pivoted on a knife-edge 57 and is biased toward a position in which contact 50 abuts contact 49 to initiate a depositing cycle. A lever 80 carrying an abutment 90 is pivoted at 81 and biased by a spring 83 into engagement with a rod 76 connected to a bellows 74, the bellows having a sensing element responsive to evaporator temperature. A lever 111 pivoted at 111a carries an abutment 116 which is urged by a spring 114 into engagement with a block 112 carried by arm 55, the lever 111 having a portion 111b which rides on the surface of a clockwise driven cam 110. When a predetermined low evaporator temperature occurs, rod 76 is retracted to allow lever 80 to pivot in a counter-clockwise direction to raise abutment 90 clear of arm 55. The latter is, however, prevented from clockwise rotation as long as portion 111b of lever 111 is riding on the high portions 117a or 117b of the cam surface and contact 50 remains in abutment with contact 52 as shown, so that the refrigeration cycle continues. When portion 111b drops into the low portions 119a or 119b of the cam surface the lever 111 pivots sufficiently to allow arm 55 to pivot into the position in which contact 50 abuts contact 49 and defrosting is initiated. Portion 111b then rides over an intermediate cam suface 118a or 118b which causes lever 111 to pivot arm 55 only to an extent which does not permit further actuation of contact 50. As the evaporator temperature rises rod 76 pivots lever 80 in a clockwise direction and as the temperature rises still further lever 80 picks up a second spring-biased lever 95 to increase the load on rod 76 so that abutment 90 does not engage arm 55 until an evaporator temperature substantially above freezing is reached. Abutment 90 then pivots arm 55 so that contact 50 moves to contact 52 and defrosting is terminated. Should abutment 90 fail to pivot arm 55 then this is effected by lever 111 when portion 111b returns to cam surface portions 117a or 117b. One of the low portions 119a, 119b may be rendered inoperative by an arm 135 as indicated at 135<SP>1</SP> so that only one defrosting cycle can be initiated per cam revolution. The biasing springs for levers 80 and 95 and the positions of abutments 90 and 116 are adjustable. The defrosting control is associated with a reversible cycle heat pump and effects defrosting by actuating the reversing valve.