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
Inputs
Outputs
AC Voltage
Heat Absorbing Refrigerant
Warm Substances
Cooled Substances

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 Temp High Pressure
Vapor
High Temp High Pressure
Liquid
Low Temp Low Pressure
Vapor
Low Temp Low 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
Condenser is silver winding tubes running through back of refrigerator
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
PROBLEM
PROBABLE CAUSE
The unit is not functioning
Blown fuse
The equipment is disconnected
There is no or low electricity in the feed circuit
The freezer is functioning continuously but is not
cooling.
The thermostat is adjusted too high
The unit contains excessive frost
The unit is showing
fluctuations in temperature.
The temperature control is not calibrated
The condenser is dirty
PROBLEM
PROBABLE CAUSE
The unit shows a high temperature
The door is open
Poor door seal
There is a defect in the electrical feed
A warm load (liquids or solids) was placed inside the unit.
The compressor is not functioning
The compressor is functioning but there is no ice in the evaporator

19. Basic Troubleshooting
PROBLEM
PROBABLE CAUSE
Upon operating the unit, noises similar to clicking
sounds can be heard
The compressor’s thermal protector has been disconnected
Noisy operation
Floor not stable or cabinet not levelled
Drip tray vibrating
The cooling fan is hitting the cover or compressor is loose
PROBLEM
PROBABLE CAUSE
The compressor runs continuously
Not enough air circulation around the unit
Faulty thermostat
Poor door seal
Room too warm
The door is being opened too often or is not closed
The light switch is defective