Abstract: A sensing device detects "flashing" in a refrigerant liquid line, upstream from the expansion valves of the evaporators of a refrigeration system. In response, a valve opens in a line extending between the compressor discharge line and a receiver, to bypass discharge vapor into the receiver, thus raising the head pressure to an extent sufficient to satisfy the requirement for a steady liquid refrigerant flow at the expansion valve. The head pressure is raised only to the minimal extent necessary to satisfy this requirement. Disclosed is a sensor of the type incorporating a sight glass in the path of a beam extending between photoelectric cells, though other sensing devices of an equivalent nature can be used. The invention can comprise a single sensing device in the liquid line extending to one or more evaporators connected in parallel.

Abstract: A commercial refrigerated display case, of the type in which an air curtain is directed across an upwardly opening product display space, utilizes ambient air for defrost purposes. A discharge sill extending along the back of the case, above the discharge grille through which air is directed to form the air curtain, is hollowly formed to provide a defrost air chamber. Within the chamber defrost air fans are mounted and are normally off during the refrigeration cycle of the display case. During defrost, the air circulating fan continues in operation although the evaporator coil is no longer in a refrigeration mode. At the same time the defrost fan goes into operation, and draws off part of the air circulated through the discharge grille by the main fan, and exhausts it to ambient through the discharge sill. A weak air curtain is still maintained across the access opening of the display case.

Abstract: Defrost of a refrigerated display case, especially those cases in which refrigerated air curtains are directed across open front or open top areas, is improved by reversing the direction of the air circulating fans during a predetermined portion of the time during which the case is in a hot gas defrost mode. In a preferred example, the evaporator fan motors are reversed following the initiation of a hot gas defrost cycle, at a time during the cycle when air warmed by the defrosting evaporator coil becomes available. A thermally actuated switch means effects the reversal at the appropriate time, so that areas of the refrigerated display case that would normally be the last to receive the benefits of the warmed air, in particular the return air flue and tank drain, become the first to be subjected to the warming effect thereof.