Abstract: An upright split door, ultra low temperature freezer which includes a single chamber cooled by a cold wall refrigeration system and accessible by separate upper and lower doors. The refrigeration system maintains the chamber at a substantially constant, ultra low temperature, such as within the range of about -50.degree. C. to -90.degree. C. Short term items may be stored in and accessed from an upper portion of the chamber by the upper door without causing the very cold air in the freezer chamber from spilling out the lower portion of the chamber. Long term items may be stored in the lower portion of the chamber and accessed by the lower door. A horizontal mullion is mounted to the freezer side walls and extends between the two doors to provide a seal for respective lower and upper edges of the two doors. A self-regulating heater strip is disposed within the mullion between upper and lower resilient sealing bulbs extending horizontally to prevent condensation build up in the mullion area.

Abstract: An upright split door, ultra low temperature freezer which includes a single chamber cooled by a cold wall refrigeration system and accessible by separate upper and lower doors. The refrigeration system maintains the chamber at a substantially constant, ultra low temperature, such as within the range of about -50.degree. C. to -90.degree. C. Short term items may be stored in and accessed from an upper portion of the chamber by the upper door without causing the very cold air in the freezer chamber from spilling out the lower portion of the chamber. Long term items may be stored in the lower portion of the chamber and accessed by the lower door. A horizontal mullion is mounted to the freezer side walls and extends between the two doors to provide a seal for respective lower and upper edges of the two doors. A self-regulating heater strip is disposed within the mullion between upper and lower resilient sealing bulbs extending horizontally to prevent condensation build up in the mullion area.

Abstract: A refrigeration system generally including a compressor, a condenser and an expansion device connected between the condenser and the low pressure, suction side of the compressor. A pressure control is disposed on the discharge or high pressure side of the compressor to selectively allow refrigerant to bleed from the high pressure side of the system. The control continuously monitors the pressure of the refrigerant discharging from the compressor and bleeds refrigerant off into a bypass, including an expansion tank and a bypass capillary tube, when a predetermined pressure is reached. The bypass capillary tube is connected between the expansion tank and the low pressure side or suction line of the system. When the control senses that the compressor discharge pressure has fallen below a preset pressure, the bleed off of refrigerant from the high pressure side of the system is stopped. Refrigerant vapor remaining in the bypass is slowly metered into the suction line due to a pressure differential therebetween.