Refridgeration Page 70-71 Flashcards
(5 cards)
- With reference to a refrigeration system
a. Describe how air is removed from a system (8)
Describe how and where refrigerant gas is added to a system (8)
- With reference to a refrigeration system
a. Describe how air is removed from a system (8)
• Change over the compressor to manual mode
• Now close the liquid stop valve after the condenser
• Pump the entire gas into the condenser by running compressor
• Stop the compressor when the suction pressure is just above zero
• Close the suction valve for compressor
• Allow the refrigerant to cool down inside the condenser
• Bleed air slowly by opening purging valve on condenser
Describe how and where refrigerant gas is added to a system (8)
To recharge system, connect a cylinder of new refrigerant to the inlet side of the compressor. You bleed it in slowly
monitoring the suction pressure of the compressor. The cylinder will get cold as the pressurised liquid is release and
changes into a gas. The condenser outlet sight glass will show an increased flow of liquid during recharge.
- With reference to a refrigeration system, state the indications of each of the following faults:
a) Air in the system (8)
b) Undercharge of refrigerant gas (8)
- With reference to a refrigeration system, state the indications of each of the following faults:
a) Air in the system (8)
• Bubbles seen within condenser sight glass
• Not able to maintain refrigeration temperature
• High pressure and temperature on the discharge side of condenser
• Fluctuating pressures
• Jerky pointer gauge
• High condenser and compressor temperature
b) Undercharge of refrigerant gas (8)
• Low discharge pressure
• Compressor Over-running (Short cycle)
• In-effective cooling
• No liquid visible within condenser sight-glass and large bubbles
• Low suction pressure
• Compressor delivery temperature high
• Machine runs for longer periods between cut out
• Not able to maintain room temperature
3A. Sketch a simple refrigeration system showing the four major components (8)
A. Sketch a simple refrigeration system showing the four major components (8)
b. State the condition of the refrigerant between each component in the sketch (3a) (8)
b. State the condition of the refrigerant between each component in the sketch (3a) (8)
• between compressor & condenser (vapour)
• between condenser & evaporator (liquid)
• between expansion valve & evaporator (saturated vapour)
• between evaporator & compressor (dry vapour)
- Describe the operation of a domestic refrigeration plant, referencing the refrigerant condition at the main
components. (12)
b. State how liquid is prevented from returning to the compressor. (4)
- Describe the operation of a domestic refrigeration plant, referencing the refrigerant condition at the main
components. (12)
• The compressor pressurises the dry refrigerant gas which is then cooled in the condenser to become high
pressure gas. The high pressure gas then exits the condenser and changes to a liquid and collects in a
reservoir tank, usually located below the condenser. The high pressure liquid is then admitted to the
evaporator through an isolating solenoid and expansion valve which reduces the pressure. The low pressure
liquid then absorbs heat through the evaporator to become low pressure gas.
b. State how liquid is prevented from returning to the compressor. (4)
• The thermostatic expansion valve bulb on the outlet of the evaporator prevents liquid returning to the
compressor
