Refrigeration Flashcards
What are the steps of the refrigeration cycle?
1) Compression - Enters as a low-pressure low-temperature gas and leaves and a high-pressure high-temperature gas.
2) Condensation - A series of coils as a heat exchanger that removes heat from the hot refrigerant gas vapour until it condenses into a saturated liquid.
3) Expansion - Entering as a low-temperature high-pressure liquid and creates a pressure drop in the refrigerant called flashing, which allows some of it to boil creating a 2-phase mixture.
4) Evaporation - The low temperature liquid flows through the coils and a fan forces air across the fins, cooling the air by absorbing the refrigerant
How does the defrost cycle work?
1) A defrost timer initiates the defrost and can be controlled on the switchboard. It will block power to the compressor and send power to the defrost heater.
2) Heater on the bottom of the coils will start up to melt the ice and frost that may have accumulated. This melted ice will collect in the condensate pan and be drained away.
3) If not timed for stopping, the defrost termination switch is connected to a thermostat on the top of the coils that will shut off the defrost cycle when it reaches a certain temperature.
What would the typical temperature of chilled water be?
12 degrees return
6 degrees delivery
Typical pressures on a refrigeration system?
Assuming R-22
17 bar HP
5 bar LP
Can be found on refrigerant charts.
What are the indications of air in an AC system?
1) Compressor outlet temperature high.
2) Condenser outlet temperature high.
3) Condenser discharge pressure high.
4) Presence of bubbles in sight glass.
5) Jerking pointer gauge.
What are the issues with air in the refrigeration system?
Air will collect in the top of the condenser and become trapped. The liquid seal will prevent air from leaving.
It will cause a reduction in condenser surface area which will lead to a high condensing pressure.
How would you drain air from a refrigeration system?
1) Change compressor to manual.
2) Close the valve after the condenser.
3) Pump all gas into condenser using the compressor.
4) Stop the compressor when suction is just above zero.
5) Close the suction on the compressor.
6) Allow refrigerant to cool inside condenser.
7) Bleed air from the purge valve on the condenser or use a gas reclaim unit.
How can air enter the system?
A leak in the low pressure side. This will lead to an undercharged system that can cause a vacuum to run that can pull more air in.
Also may enter through poor fittings and connections, poor charging or recovery or forgetting to purge hoses.
What are the main refrigerants used on board?
R404A and R134
What is the montreal protocol?
The remove of CFC’s.
What can frosting mean on the compressor?
Liquid coming into the compressor. Needs to be superheated after evaporator to prevent liquid forming as you cannot compress it.
What can bubbling in the sight-glass mean?
Air in the system or insufficient refrigerant.
What could a higher discharge pressure mean?
Condenser blocked as we are not cooling the refrigerant.
What is the purpose of the filter drier?
To remove moisture from the system.
What would be cut-outs on the compressor?
1) HP
2) LP
3) Differential for LO
4) Relief valve on compressor
5) Defrost cycle
