Refrigeration Air Conditioning
Work Ready Certification with
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Define subcooling - ANSWER - Subcooling is the process by which a saturated liquid
refrigerant is cooled below the saturation temperature, forcing it to change its
phase completely
Using a three positions liquid line service valve, when is the front seated position
used? - ANSWER - When the system is to be pumped down
the external equalizer line should be located..? - ANSWER - The bulb should be
mounted on a horizontal portion of the line, 6" to 8" downstream from the TXV
sensing bulb.
When the portion of a pressure-enthalpy diagram is beneath the saturation curve
then..? - ANSWER - refrigerant follows a temperature/ pressure relationship.
TXV controls..? - ANSWER - Evaporator superheat by controlling refrigerant flow into
the evaporator
When using a water cooled condenser, an increase of cold water will..? - ANSWER -
Decrease the power consumption of the compressor
How many BTUs are required to change one pound of ice at 20 degrees F to steam
at 220 degrees F? - ANSWER - - From 20 °F to 32°F = 6 Btu (sensible heat, 0.5 per 1
°F )
- Solid to liquid (32°F) = 144 Btu (latent heat)
- From 32 °F to 212°F = 180 Btu (sensible heat)
- Liquid to steam (212°F)= 970 Btu (latent heat)
- From 212 °F to 220°F = 4 Btu (sensible heat, 0.5 per 1 °F)
, TOTAL= 1304 Btu
A manifold gauge is properly connected to the suction and discharge valves on a
compressor, in order to read the high and low side, what position should the gauge
manifold valves be in? - ANSWER - n order to read the high and low side pressures
in the system, the valves should be fully clockwise
Where is the "king" valve located? - ANSWER - found downstream from a liquid line
receiver, outlet of liquid line receiver.
List three things that might be indicated by bubble in a liquid line sight glass. -
ANSWER - undercharge, plugged filter drier on liquid line, or air in the system.
What system conditions will result from a partially plugged cap tube metering
device? - ANSWER - High head pressure, low suction pressure, high subcool &
superheat
What conditions will result from a refrigerant overcharge in a refrigeration system? -
ANSWER - Higher suction and head pressure, higher subcool, lower superheat,
higher amp draw on compressor due to more work.
When a TXV is used on a large evaporator or an evaporator with a pressure drop of
6 to 7 pounds across the evaporator, the valve will prematurely cause "hunting"
(valve fluctuates toward opening and closing.) In the case of valve hunting, to solve
this issue should be installed a TXV equipped with..? - ANSWER - The external
equalizer line compensates for a pressure drop from the inlet of the evaporator to
the end of the tail coil and eliminates valve hunting.
The equalizer line must be located downstream from the sensing bulb.
To what relationship does refrigerant correspond to ONLY in its saturated state? -
ANSWER - Pressure temperature relationship. When not in its saturated state it no
longer corresponds to this relationship and is either subcooled or superheated
Work Ready Certification with
Complete Solutions
Define subcooling - ANSWER - Subcooling is the process by which a saturated liquid
refrigerant is cooled below the saturation temperature, forcing it to change its
phase completely
Using a three positions liquid line service valve, when is the front seated position
used? - ANSWER - When the system is to be pumped down
the external equalizer line should be located..? - ANSWER - The bulb should be
mounted on a horizontal portion of the line, 6" to 8" downstream from the TXV
sensing bulb.
When the portion of a pressure-enthalpy diagram is beneath the saturation curve
then..? - ANSWER - refrigerant follows a temperature/ pressure relationship.
TXV controls..? - ANSWER - Evaporator superheat by controlling refrigerant flow into
the evaporator
When using a water cooled condenser, an increase of cold water will..? - ANSWER -
Decrease the power consumption of the compressor
How many BTUs are required to change one pound of ice at 20 degrees F to steam
at 220 degrees F? - ANSWER - - From 20 °F to 32°F = 6 Btu (sensible heat, 0.5 per 1
°F )
- Solid to liquid (32°F) = 144 Btu (latent heat)
- From 32 °F to 212°F = 180 Btu (sensible heat)
- Liquid to steam (212°F)= 970 Btu (latent heat)
- From 212 °F to 220°F = 4 Btu (sensible heat, 0.5 per 1 °F)
, TOTAL= 1304 Btu
A manifold gauge is properly connected to the suction and discharge valves on a
compressor, in order to read the high and low side, what position should the gauge
manifold valves be in? - ANSWER - n order to read the high and low side pressures
in the system, the valves should be fully clockwise
Where is the "king" valve located? - ANSWER - found downstream from a liquid line
receiver, outlet of liquid line receiver.
List three things that might be indicated by bubble in a liquid line sight glass. -
ANSWER - undercharge, plugged filter drier on liquid line, or air in the system.
What system conditions will result from a partially plugged cap tube metering
device? - ANSWER - High head pressure, low suction pressure, high subcool &
superheat
What conditions will result from a refrigerant overcharge in a refrigeration system? -
ANSWER - Higher suction and head pressure, higher subcool, lower superheat,
higher amp draw on compressor due to more work.
When a TXV is used on a large evaporator or an evaporator with a pressure drop of
6 to 7 pounds across the evaporator, the valve will prematurely cause "hunting"
(valve fluctuates toward opening and closing.) In the case of valve hunting, to solve
this issue should be installed a TXV equipped with..? - ANSWER - The external
equalizer line compensates for a pressure drop from the inlet of the evaporator to
the end of the tail coil and eliminates valve hunting.
The equalizer line must be located downstream from the sensing bulb.
To what relationship does refrigerant correspond to ONLY in its saturated state? -
ANSWER - Pressure temperature relationship. When not in its saturated state it no
longer corresponds to this relationship and is either subcooled or superheated
