Unit 9 - Chapter 4 - Refrigeration
Operation and Maintenance Exam
Questions with Correct Answers
Pressure gauges - Answer-Indicate the conditions inside a refrigeration system. Show
evaporator and condenser pressures, they indicate saturation temps.
Does CSA B52 require permanently installed pressure gauges on any refrigeration
system? - Answer-No, it does not require them. But ammonia systems usually have
permanently installed gauges. One to the high side and one to the low side.
What should pressure gauges in a refrigeration system be equipped with? - Answer-
Pulsation dampeners to prevent flickering of the pointers due to pressure pulsations.
What is used to measure oil pressure in a refrigeration system? - Answer-Oil pressure
differential, subtract the compressor suction pressure form the oil pressure on the
gauge.
Pressure gauges on low capacity commercial refrigeration systems aren't usually
installed? - Answer-Not usually installed but have provision for attaching them.
Accumulator - Answer-A simple liquid trap located in the compressor suction line. It
collects and hold liquid so it doesn't enter the compressor. Must not be insulated, this is
so heat can be absorbed through wall. Heat vaporizes the trapped liquid and returns it
to the compressor suction.
Oil Separator - Answer-"high side" removes the oil entrained in the discharge gas and
returns it to the compressor crankcase. Reduces the need for additional oil.
What happens if oil isn't separated from refrigerant? - Answer-It will coat the condenser
and impede heat transfer.
Where does the oil go in an oil separator? - Answer-Once in the separator, refrigerant
vapour is given a sudden change of direction. Entrained oil droplets thrown out of the
vapour stream and collected at the bottom of separator and returned to compressor
crankcase.
When is it only possible to collect oil from oil-miscible refrigerants? (HFCs and HCFCs) -
Answer-Only while they are in the vapour state.
How do you prevent HFCs and HCFCs from condensing and draining to the crankcase
with the oil? - Answer-Trap must be kept hotter than the condensing temp. Place the
separator close to the compressor, and protect it from cold air drafts.
, Suction Strainer - Answer-Installed in compressor suction lines to keep particles from
entering compressors. Can be removed for cleaning without disruption.
Filter-drier - Answer-removes moisture and contaminants from refrigerant. Also,
removes particulate and scale before it flows to metering device.
What happens if moisture get into refrigerant? - Answer-Ice buildup in metering device,
acid formation causing corrosion, sludge formation, deterioration of motor insulation.
Sight glass - Answer-Located on the liquid line, bubbles indicate pressure drop.
How is moisture detected with the use of a sight glass in refrigerant? - Answer-Dye,
moisture indicator, is usually combined with the site glass. Indicator is simply of a
chemical dot placed under the sight glass lens so it is exposed to the liquid. Changes
colour if moisture is present.
Where will the sight glass be installed if used to indicate whether the system is fully
charged? - Answer-At the receiver or liquid receiver outlet.
Where should the site glass be if used to indicate if the refrigerant contains any flash
vapour? - Answer-Glass is installed before the expansion valve.
Economizer - Answer-used to transfer heat from the relatively warm liquid flowing to the
evaporator to the vapour being drawn from the evaporator.
3 Reasons economizers are used - Answer-Reduce the temp of the liquid refrigerant.
This reduces the amount of flash gas generated in the evaporator, increasing
evaporator capacity.
They prevent flashing of the liquid due to the pressure drop that occurs as the
refrigerant flows through the liquid line.
They increase the temp of the vapour passing through the economizer.
Distributor - Answer-Placed in the liquid line directly downstream from the expansion
valve, ensures each coil is fed refrigerant equally.
Vibration Absorber - Answer-By connecting the piping to the main components of the
refrigeration system using these, transmission of vibration and noise is prevented.
What is dependant on the type of piping used in the refrigeration system? - Answer-Size
of piping and tubing required, the refrigerant used and the application.
According to ASME B31.5 what materials can be used for a refrigeration system? -
Answer-All materials must be suitable for low temp service. Materials that become brittle
under low temp can not be used, as well has to be compatible with refrigerant.
Operation and Maintenance Exam
Questions with Correct Answers
Pressure gauges - Answer-Indicate the conditions inside a refrigeration system. Show
evaporator and condenser pressures, they indicate saturation temps.
Does CSA B52 require permanently installed pressure gauges on any refrigeration
system? - Answer-No, it does not require them. But ammonia systems usually have
permanently installed gauges. One to the high side and one to the low side.
What should pressure gauges in a refrigeration system be equipped with? - Answer-
Pulsation dampeners to prevent flickering of the pointers due to pressure pulsations.
What is used to measure oil pressure in a refrigeration system? - Answer-Oil pressure
differential, subtract the compressor suction pressure form the oil pressure on the
gauge.
Pressure gauges on low capacity commercial refrigeration systems aren't usually
installed? - Answer-Not usually installed but have provision for attaching them.
Accumulator - Answer-A simple liquid trap located in the compressor suction line. It
collects and hold liquid so it doesn't enter the compressor. Must not be insulated, this is
so heat can be absorbed through wall. Heat vaporizes the trapped liquid and returns it
to the compressor suction.
Oil Separator - Answer-"high side" removes the oil entrained in the discharge gas and
returns it to the compressor crankcase. Reduces the need for additional oil.
What happens if oil isn't separated from refrigerant? - Answer-It will coat the condenser
and impede heat transfer.
Where does the oil go in an oil separator? - Answer-Once in the separator, refrigerant
vapour is given a sudden change of direction. Entrained oil droplets thrown out of the
vapour stream and collected at the bottom of separator and returned to compressor
crankcase.
When is it only possible to collect oil from oil-miscible refrigerants? (HFCs and HCFCs) -
Answer-Only while they are in the vapour state.
How do you prevent HFCs and HCFCs from condensing and draining to the crankcase
with the oil? - Answer-Trap must be kept hotter than the condensing temp. Place the
separator close to the compressor, and protect it from cold air drafts.
, Suction Strainer - Answer-Installed in compressor suction lines to keep particles from
entering compressors. Can be removed for cleaning without disruption.
Filter-drier - Answer-removes moisture and contaminants from refrigerant. Also,
removes particulate and scale before it flows to metering device.
What happens if moisture get into refrigerant? - Answer-Ice buildup in metering device,
acid formation causing corrosion, sludge formation, deterioration of motor insulation.
Sight glass - Answer-Located on the liquid line, bubbles indicate pressure drop.
How is moisture detected with the use of a sight glass in refrigerant? - Answer-Dye,
moisture indicator, is usually combined with the site glass. Indicator is simply of a
chemical dot placed under the sight glass lens so it is exposed to the liquid. Changes
colour if moisture is present.
Where will the sight glass be installed if used to indicate whether the system is fully
charged? - Answer-At the receiver or liquid receiver outlet.
Where should the site glass be if used to indicate if the refrigerant contains any flash
vapour? - Answer-Glass is installed before the expansion valve.
Economizer - Answer-used to transfer heat from the relatively warm liquid flowing to the
evaporator to the vapour being drawn from the evaporator.
3 Reasons economizers are used - Answer-Reduce the temp of the liquid refrigerant.
This reduces the amount of flash gas generated in the evaporator, increasing
evaporator capacity.
They prevent flashing of the liquid due to the pressure drop that occurs as the
refrigerant flows through the liquid line.
They increase the temp of the vapour passing through the economizer.
Distributor - Answer-Placed in the liquid line directly downstream from the expansion
valve, ensures each coil is fed refrigerant equally.
Vibration Absorber - Answer-By connecting the piping to the main components of the
refrigeration system using these, transmission of vibration and noise is prevented.
What is dependant on the type of piping used in the refrigeration system? - Answer-Size
of piping and tubing required, the refrigerant used and the application.
According to ASME B31.5 what materials can be used for a refrigeration system? -
Answer-All materials must be suitable for low temp service. Materials that become brittle
under low temp can not be used, as well has to be compatible with refrigerant.
