HVAC Unit 25 Special Refrigeration
System Components ACTUAL UPDATED
QUESTIONS AND CORRECT ANSWERS
What categories are special refrigeration system components divided into? - CORRECT
ANSWERS✅✅Controls and accessories.
What categories are control components divided into? - CORRECT
ANSWERS✅✅Mechanical, electrical and electromechanical.
What do mechanical controls generally do and how do they do it? Where are they usually
found? - CORRECT ANSWERS✅✅They stop, start or modulate fluid flow and are operated
by pressure, temperature, and electricity. They are usually found in the piping.
Describe an EPR valve. - CORRECT ANSWERS✅✅An evaporator pressure-regulating
valve is a mechanical control that keeps refrigerant pressure in the evaporator from going
below a predetermined point.
What is another name for a holdback valve? - CORRECT ANSWERS✅✅An EPR is called
a holdback valve because it holds refrigerant back in the evaporator in order to keep the
suction pressure above a set point.
How does an EPR work? - CORRECT ANSWERS✅✅There is a spring attached to a disc.
When the pressure is above the set point, there is enough pressure to push the disc and spring
in and keep the EPR open and refrigerant can flow freely from the evaporator to the suction
line. If the pressure drops below the preset point, the pressure is not enough to push and open
the disc/spring and it closes. While it is closed, the evaporator starts to build up pressure since
the TXV is still metering refrigerant to it. Once the pressure rises above the set point, it is
able to push the disc/spring and open the valve and allow the refrigerant to flow again.
What are the two forces in an EPR? - CORRECT ANSWERS✅✅The evaporator pressure
and the pressure of the spring.
T or F - The spring pressure is a opening force. - CORRECT ANSWERS✅✅False, it is a
closing force.
, For a system with multiple evaporators, what is used instead of an EPR on the lowest
temperature evaporator to keep refrigerant from flowing into it? - CORRECT
ANSWERS✅✅A check valve.
What is an EEPR and how does it differ from an EPR? - CORRECT ANSWERS✅✅EEPR
stands for electric evaporator pressure regulating valve. It is operated by a bipolar step motor
that provides very close temperature control of the discharge air in supermarket display cases.
They can move in very small increments, either opening or closing the suction line in
response to the discharge air temperature.
What is a CPR? - CORRECT ANSWERS✅✅It stands for crankcase pressure-regulating
valve. It is in the suction line close to the compressor and is used to keep low-temperature
compressors from overloading during a hot pulldown.
What are the three occurrences for a hot pulldown? - CORRECT ANSWERS✅✅1. When
the compressor has been off for a long time and the foodstuff has a rise in temp
2. On startup of a warm box
3. After a defrost period.
What are relief valves and what types do they come in? - CORRECT ANSWERS✅✅Relief
valves are designed to release refrigerant from a system when predetermined high pressure
exists. They come in spring-loaded type (that reseats itself) and one-time type (that does not
close back).
What is the purpose of a low-ambient control? - CORRECT ANSWERS✅✅Its purpose is to
keep head pressure up when the ambient air temperature is low like during the winter.
Name the four methods for low-ambient control - CORRECT ANSWERS✅✅1. Fan cycling
using a pressure control
2. Fan speed control
3. Air volume control using shutters and fan cycling
4. Condenser flooding devices
System Components ACTUAL UPDATED
QUESTIONS AND CORRECT ANSWERS
What categories are special refrigeration system components divided into? - CORRECT
ANSWERS✅✅Controls and accessories.
What categories are control components divided into? - CORRECT
ANSWERS✅✅Mechanical, electrical and electromechanical.
What do mechanical controls generally do and how do they do it? Where are they usually
found? - CORRECT ANSWERS✅✅They stop, start or modulate fluid flow and are operated
by pressure, temperature, and electricity. They are usually found in the piping.
Describe an EPR valve. - CORRECT ANSWERS✅✅An evaporator pressure-regulating
valve is a mechanical control that keeps refrigerant pressure in the evaporator from going
below a predetermined point.
What is another name for a holdback valve? - CORRECT ANSWERS✅✅An EPR is called
a holdback valve because it holds refrigerant back in the evaporator in order to keep the
suction pressure above a set point.
How does an EPR work? - CORRECT ANSWERS✅✅There is a spring attached to a disc.
When the pressure is above the set point, there is enough pressure to push the disc and spring
in and keep the EPR open and refrigerant can flow freely from the evaporator to the suction
line. If the pressure drops below the preset point, the pressure is not enough to push and open
the disc/spring and it closes. While it is closed, the evaporator starts to build up pressure since
the TXV is still metering refrigerant to it. Once the pressure rises above the set point, it is
able to push the disc/spring and open the valve and allow the refrigerant to flow again.
What are the two forces in an EPR? - CORRECT ANSWERS✅✅The evaporator pressure
and the pressure of the spring.
T or F - The spring pressure is a opening force. - CORRECT ANSWERS✅✅False, it is a
closing force.
, For a system with multiple evaporators, what is used instead of an EPR on the lowest
temperature evaporator to keep refrigerant from flowing into it? - CORRECT
ANSWERS✅✅A check valve.
What is an EEPR and how does it differ from an EPR? - CORRECT ANSWERS✅✅EEPR
stands for electric evaporator pressure regulating valve. It is operated by a bipolar step motor
that provides very close temperature control of the discharge air in supermarket display cases.
They can move in very small increments, either opening or closing the suction line in
response to the discharge air temperature.
What is a CPR? - CORRECT ANSWERS✅✅It stands for crankcase pressure-regulating
valve. It is in the suction line close to the compressor and is used to keep low-temperature
compressors from overloading during a hot pulldown.
What are the three occurrences for a hot pulldown? - CORRECT ANSWERS✅✅1. When
the compressor has been off for a long time and the foodstuff has a rise in temp
2. On startup of a warm box
3. After a defrost period.
What are relief valves and what types do they come in? - CORRECT ANSWERS✅✅Relief
valves are designed to release refrigerant from a system when predetermined high pressure
exists. They come in spring-loaded type (that reseats itself) and one-time type (that does not
close back).
What is the purpose of a low-ambient control? - CORRECT ANSWERS✅✅Its purpose is to
keep head pressure up when the ambient air temperature is low like during the winter.
Name the four methods for low-ambient control - CORRECT ANSWERS✅✅1. Fan cycling
using a pressure control
2. Fan speed control
3. Air volume control using shutters and fan cycling
4. Condenser flooding devices
