Refrigerators

Topics

Applications Principles of Operation Diagrams Safety Preventive Maintenance Common Failure Modes Basic Troubleshooting

Applications

In laboratory or medical setting, used to keep medicines and chemicals cool

Principle of Operation Inputs Outputs

AC Voltage Heat Absorbing Refrigerant

Warm Substances Cooled Substances

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

Principles of Operation

High TempHigh PressureVapor

High TempHigh PressureLiquid

Low TempLow PressureVapor

Low TempLow PressureLiquid

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.

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

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

Principles of Operation

Electrical Components Compressor Thermostat Overload protector

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)

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

Diagrams

Cold Line (inlet) (Suction

line)

Compressor

Hot line (outlet) (compressor discharge

line) Electrical

Wire Housing

Overload Protector

Grounding Plate

Liquid Line

Expansion Valve

Drying Assembly

Power Cord

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

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

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

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

Basic TroubleshootingPROBLEM 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 notcooling.

• 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

Basic Troubleshooting PROBLEM PROBABLE CAUSE

Upon operating the unit, noises similar to clickingsounds 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