Refrigerators

1. Refrigerators

2. Topics • Applications • Principles of Operation • Diagrams • Safety • Preventive Maintenance • Common Failure Modes • Basic Troubleshooting

3. Applications • In laboratory or medical setting, used to keep medicines and chemicals cool

4. Principle of Operation

5. Principles of Operation • Refrigerant cycles through a sealed system of high and low pressures, releasing and absorbing heat • Refrigeration: Absorption of heat during the evaporation of a liquid refrigerant • Four main components • Compressor • Condenser • Expansion Valve/Metering Device • Evaporator

6. Principles of Operation High TempHigh Pressure Vapor High TempHigh Pressure Liquid Low TempLow Pressure Vapor Low TempLow Pressure Liquid

7. Principles of Operation • Compressor • The refrigerant is compressed into a high pressure, high temperature vapor • Condenser • As refrigerant passes through the condensing coils heat moves from the refrigerant to the surrounding air causing it to condense. • The refrigerant leaves the condenser as a high pressure, high temperature liquid.

8. Principles of Operation • Metering Device • Regulates how much liquid refrigerant enters the evaporator • Tries to maintain a preset temperature difference on either side of the evaporator opening

9. Principles of Operation • Evaporator • Metering device allows small amount of refrigerant into evaporator • Refrigerant rapidly expands, cools • At beginning of the evaporator refrigerant is a low pressure, low temperature liquid • As refrigerant passes through evaporator, it pulls heat out of refrigerator causing refrigerant to slowly evaporate back into a vapor • The refrigerant returns to the compressor as low pressure, low temperature vapor

10. Principles of Operation • Electrical Components • Compressor • Thermostat • Overload protector

11. Principles of Operation • Compressor • Motor and compressor are in one unit and is known as a sealed unit • Single phase induction motor • Contains two windings • Starter (S) • Main (M)

12. Principles of Operation • Overload Protector • A thermal device which opens the circuit of the motor when overloaded • Prevents damage to the motor when PTC prevents starting, but current is sent to motor’s main winding

13. Diagrams Hot line (outlet) (compressor discharge line) Electrical Wire Housing Expansion Valve Compressor Drying Assembly Liquid Line Overload Protector Cold Line (inlet) (Suction line) Grounding Plate Power Cord

14. Safety • Never puncture any line containing refrigerant • Never use a sharp object to chip ice off of evaporator • Allow ice to melt naturally or use a hair dryer • Use PPE if refrigerator is used to store biological hazards • Before using, read the owner's manual

15. Operation • Never connect a unit to an overloaded electrical outlet or one with voltage deficiencies • Avoid the use of electrical extension cords • The electrical outlet must not be more than 2 m from the unit • Install the unit on a levelled surface • Leave free space around unit to avoid over heating • Do not install under direct sun light

16. Preventive Maintenance • If connected to good quality electrical circuits and good ventilation flows around the unit, refrigerators function for years without specialized technical maintenance • Clean inside of refrigerator box • Avoid using steel wool or other abrasive materials for cleaning the shelves and drawers • Avoid using gasoline, naphtha or thinners, as these damage the plastic, the packing or the paint on the surfaces. • Check door gasket fully seals door

17. Common Failures • Blown fuse • Bad power connection • Evaporator covered in ice • Condenser is blocked or dirty • Door does not close properly • Failed overload protector • User Error: improper setup/placement • Faulty thermostat

18. Basic Troubleshooting

19. Basic Troubleshooting