HVACR318 – Refrigeration II

1. HVACR318 – Refrigeration II Domestic Freezers

2. The Domestic Freezer, Overview • Characteristics: • One temperature appliance (low temperature) • Take longer to freeze food than commercial freezers • Food must be packed correctly • Functions: • Store food that was purchased frozen • Freeze small amounts of food

3. The Cabinet or Box • Sheet-metal exterior with plastic interior. Two types or styles: • Upright • Takes up less space • Usually located in the kitchen • Chest type • More efficient than upright units • Cold air stays in the box

4. Vertical Configuration

5. Horizontal (Chest) Configuration

6. Air Flow Inside Vertical Unit Warmer air fills the box Heavier, cooler air falls from the box

7. Air Flow Inside Horizontal Unit Heavier, cold air stays in the chest-type freezer, even when the lid is open

8. Cabinet Interior • Characteristics: • Can be metal or plastic • Walls are insulated with fiberglass or foam • Broken plastic should be repaired • Gaskets must remain tight fitting • Air leaks will cause excessive compressor run time

9. Door Gasket Leaks Warm air can leak into the box if the door gaskets are defective

10. The Evaporator • Forced-draft type • Uses a propeller or centrifugal blower • Plate type or tube type • No fan is used • Must be manually defrosted • Freezer wall plate • Tubing attached to the interior of the box walls

11. Freezer Shelf Design FREEZER SHELVES Wire shelves with refrigerant tubing Stamped plate evaporators

12. The Compressor • Can be rotary or reciprocating • Located at the back of the unit on the bottom • Some units have condensing unit on a slide out tray • Hermetically sealed, welded compressors

13. Compressor and Condenser Condensing unit can be on a slide out shelf Compressor compartment of a vertical freezer

14. The Condenser • Home units always have air-cooled condensers; there are three types: • Chimney type • Must be enough airflow across it • Hot-wall type • Condenser located inside the walls • Forced-draft type • Usually used on automatic defrost units

15. Natural-draft condenser Compressor Suction line Back View of Freezer Unit Back of freezer

16. Compressor Hot Wall Condenser Back of freezer Discharge line from compressor run within the insulated walls of the freezer box Liquid line

17. The Metering Device • Capillary tube is most typical • Fastened to the suction line • Provides liquid floodback protection • Increases the subcooling • Can also be located inside the suction line

18. Capillary Tube Capillary Tube Diagram Suction Line Capillary tube connected to the suction line Capillary tube run inside the suction line

19. Capillary Tube Cross Section Capillary Tube Suction Line High Temperature, High Pressure Refrigerant Heat is transferred from the refrigerant in the capillary tube to the refrigerant in the suction line Suction Gas

20. Typical Operating Conditions: Evaporator • Must be cold enough to freeze ice cream hard • When the box temperature is 0° • Coil can be -18° for a plate type • 2.2 in. Hg for 134a • 1.3 psig for R-12 • Coil can be -11° for a forced-draft type • 1.2 psig for R-134a • 4 psig for R-12

21. Typical Operating Conditions: Condenser • Condensers are air cooled • Natural or forced draft • Design ambient temperature from 65° to 95° • Condensing temperature is 25° to 35° higher than ambient

22. Typical Operating Conditions: Compressor • Compressor should be hot to the touch • Air-cooled compressors have fins • Should operate quietly • Usually mounted on rubber feet • Extra load on the compressor can be one caused by gasket leaks or constant opening of the box

23. Freezer Controls • Typical freezers have a thermostat and door switch • Wiring diagrams are usually fastened to the box • Small heaters prevent cabinet sweating • Automatic defrost • Controls similar to a refrigerator • Compressor run time can start defrost cycle • Electric heaters can be used for defrost

24. Mullion Heater Thermostat Defrost Timer M Defrost Heater Evaporator Fan Motor M C S Overload Line Cord Compressor R Relay Domestic Freezer Wiring Diagram

25. Forced Draft Evaporator

26. Electric Strip Heater Electric strip heater in contact with the evaporator coil

27. Servicing the Freezer • Forced-draft evaporator motors • Run whenever compressor is on • Can be controlled by a door switch • Often utilize automatic defrost (hot gas or electric heaters) • Manual defrost • Pan of hot water or blow drier (heat gun) • Do not use sharp objects to defrost a coil!

28. Moving the Freezer • Remove food from freezer before servicing or moving it. • Use caution when moving any heavy equipment. • Wear a back brace if available. • Lift with the legs, not the back. • Use a hand truck if available. • Never lay a freezer on its side, which can cause damage to freezer components.

29. Temporary Food Storage • Some companies offer loaner boxes • Use dry ice if possible: • Product can be stored in boxes with a protective layer between food and dry ice • 20 lbs of dry ice is used for every 5 cubic feet of freezer capacity for a 24-hour period

30. Summary 1 • The domestic freezer is a one-temperature (low) appliance. • Upright or chest-type configuration; chest-type is more efficient than upright models. • Air leakage increases compressor run time. • The evaporator can be forced draft, plate-type or freezer wall plate. • Compressors are typically rotary or hermetically sealed.

31. Summary 2 • Domestic freezers use air-cooled condensers. • Condensers can be chimney type, hot wall or forced draft. • The metering device found on domestic freezers is the capillary tube. • The capillary tube can be secured to the suction line or run inside the suction line itself. • The evaporator can be manual or automatic defrost.