Download Lecture 4 Refrigerator

Refrigerators
Topics
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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
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Compressor
Condenser
Expansion Valve/Metering Device
Evaporator
Principles of Operation
High Temp
High Pressure
Vapor
High Temp
High Pressure
Liquid
Low Temp
Low Pressure
Vapor
Low Temp
Low Pressure
Liquid
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
Expansion
Valve
Electrical
Wire
Housing
Hot line (outlet)
(compressor discharge
line)
Compressor
Drying
Assembly
Liquid Line
Cold Line
Power
Cord (inlet) (Suction
line)
Overload
Protector
Grounding
Plate
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
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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 Troubleshooting
PROBLEM
PROBABLE CAUSE
The unit is not
functioning
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The freezer is
functioning
continuously but
is not
cooling.
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The unit is
showing
fluctuations in
temperature.
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Blown fuse
The equipment is
disconnected
There is no or
low electricity in
the feed circuit
The thermostat
is adjusted too
high
The unit contains
excessive frost
The temperature
control is not
calibrated
The condenser is
dirty
PROBLEM
PROBABLE CAUSE
The unit shows a
high
temperature
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The door is open
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Poor door seal
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There is a defect
in the electrical
feed
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A warm load
(liquids or solids)
was placed inside
the unit.
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The compressor is
not functioning
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The compressor is
functioning but
there is no ice in
the evaporator
Basic Troubleshooting
PROBLEM
Upon operating the
unit, noises similar
to clicking
sounds can be heard
Noisy operation
PROBABLE CAUSE
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The compressor’s
thermal protector
has been
disconnected
Floor not stable or
cabinet not
levelled
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Drip tray vibrating
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The cooling fan is
hitting the cover
or compressor is
loose
PROBLEM
PROBABLE CAUSE
The compressor
runs
continuously
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Not enough air
circulation around
the unit
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Faulty thermostat
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Poor door seal
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Room too warm
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The door is being
opened too often or
is not closed
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The light switch is
defective