, Question 1
A parallel rack system with three compressors and a common discharge header
exhibits fluctuating discharge pressure and high superheat at the evaporators.
Which control strategy best addresses this while maintaining energy
efficiency?
A. Adjust each compressor's unloader to maintain a constant suction
pressure setpoint.
B. Implement floating suction pressure control based on the highest
evaporator load.
C. Set a fixed discharge pressure setpoint and modulate condenser fans
accordingly.
D. Use a mechanical subcooling circuit to reduce flash gas in the liquid
line.
Correct Answer: B - Implement floating suction pressure control
based on the highest evaporator load.
RATIONALE
Floating suction pressure control optimizes compressor loading by
adjusting to the highest evaporator demand, reducing energy use while
stabilizing superheat. Fixed setpoints or unloader adjustments can
cause inefficiency. Mechanical subcooling addresses liquid line issues,
not suction fluctuations.
Question 2
During a retrofit from R-22 to R-448A in a low-temperature system, the
technician observes increased compressor discharge temperature. Which factor
most likely contributes to this?
A. R-448A has a higher latent heat of vaporization than R-22.
B. The existing mineral oil is incompatible with R-448A, causing poor
lubrication.
C. R-448A has a higher global warming potential, requiring different
Page 2
, expansion valve settings.
D. The system's condenser is undersized for the new refrigerant's higher
volumetric capacity.
Correct Answer: D - The system's condenser is undersized for the
new refrigerant's higher volumetric capacity.
RATIONALE
R-448A has a higher volumetric cooling capacity, which can lead to
increased discharge temperatures if the condenser cannot reject the
additional heat. Incompatible oil would cause lubrication issues, not
directly higher discharge temperatures. Latent heat and GWP do not
directly cause higher discharge temperatures.
Question 3
An electronically commutated motor (ECM) evaporator fan in a walk-in cooler
is drawing higher-than-normal current and running at reduced speed. Which is
the most probable cause?
A. A failed start capacitor causing the motor to slip.
B. A shorted run winding in the motor stator.
C. A blocked or restricted return air path increasing static pressure.
D. A faulty thermistor in the motor control module.
Correct Answer: C - A blocked or restricted return air path
increasing static pressure.
RATIONALE
ECMs adjust speed based on static pressure; a blocked return air path
increases resistance, causing the motor to draw more current and slow
down. Capacitor or winding failures typically cause no-start or erratic
operation. A faulty thermistor would likely trigger an error code or
shutdown.
Page 3
, Question 4
A transcritical CO2 booster system in a supermarket operates with a gas cooler
pressure of 110 bar and ambient temperature of 35°C. Which adjustment would
most improve system efficiency?
A. Increase the gas cooler pressure to 120 bar to enhance subcooling.
B. Decrease the gas cooler pressure to 90 bar to reduce compressor work.
C. Activate the parallel compression to bypass the high-stage compressor.
D. Adjust the expansion valve to maintain a higher evaporator superheat.
Correct Answer: B - Decrease the gas cooler pressure to 90 bar to
reduce compressor work.
RATIONALE
In transcritical CO2 systems, lowering gas cooler pressure reduces
compressor work and improves efficiency when ambient temperature
is moderate. Increasing pressure would raise energy use. Parallel
compression helps at high ambient, but here pressure reduction is
more direct. Higher superheat reduces capacity.
Question 5
A technician is troubleshooting a refrigeration system with a thermostatic
expansion valve (TXV) that is hunting. Which condition is least likely to cause
this?
A. An oversized TXV relative to the evaporator load.
B. A partially restricted liquid line filter drier.
C. A superheat setting that is too low.
D. A faulty evaporator pressure regulator (EPR) valve.
Correct Answer: D - A faulty evaporator pressure regulator
(EPR) valve.
Page 4
A parallel rack system with three compressors and a common discharge header
exhibits fluctuating discharge pressure and high superheat at the evaporators.
Which control strategy best addresses this while maintaining energy
efficiency?
A. Adjust each compressor's unloader to maintain a constant suction
pressure setpoint.
B. Implement floating suction pressure control based on the highest
evaporator load.
C. Set a fixed discharge pressure setpoint and modulate condenser fans
accordingly.
D. Use a mechanical subcooling circuit to reduce flash gas in the liquid
line.
Correct Answer: B - Implement floating suction pressure control
based on the highest evaporator load.
RATIONALE
Floating suction pressure control optimizes compressor loading by
adjusting to the highest evaporator demand, reducing energy use while
stabilizing superheat. Fixed setpoints or unloader adjustments can
cause inefficiency. Mechanical subcooling addresses liquid line issues,
not suction fluctuations.
Question 2
During a retrofit from R-22 to R-448A in a low-temperature system, the
technician observes increased compressor discharge temperature. Which factor
most likely contributes to this?
A. R-448A has a higher latent heat of vaporization than R-22.
B. The existing mineral oil is incompatible with R-448A, causing poor
lubrication.
C. R-448A has a higher global warming potential, requiring different
Page 2
, expansion valve settings.
D. The system's condenser is undersized for the new refrigerant's higher
volumetric capacity.
Correct Answer: D - The system's condenser is undersized for the
new refrigerant's higher volumetric capacity.
RATIONALE
R-448A has a higher volumetric cooling capacity, which can lead to
increased discharge temperatures if the condenser cannot reject the
additional heat. Incompatible oil would cause lubrication issues, not
directly higher discharge temperatures. Latent heat and GWP do not
directly cause higher discharge temperatures.
Question 3
An electronically commutated motor (ECM) evaporator fan in a walk-in cooler
is drawing higher-than-normal current and running at reduced speed. Which is
the most probable cause?
A. A failed start capacitor causing the motor to slip.
B. A shorted run winding in the motor stator.
C. A blocked or restricted return air path increasing static pressure.
D. A faulty thermistor in the motor control module.
Correct Answer: C - A blocked or restricted return air path
increasing static pressure.
RATIONALE
ECMs adjust speed based on static pressure; a blocked return air path
increases resistance, causing the motor to draw more current and slow
down. Capacitor or winding failures typically cause no-start or erratic
operation. A faulty thermistor would likely trigger an error code or
shutdown.
Page 3
, Question 4
A transcritical CO2 booster system in a supermarket operates with a gas cooler
pressure of 110 bar and ambient temperature of 35°C. Which adjustment would
most improve system efficiency?
A. Increase the gas cooler pressure to 120 bar to enhance subcooling.
B. Decrease the gas cooler pressure to 90 bar to reduce compressor work.
C. Activate the parallel compression to bypass the high-stage compressor.
D. Adjust the expansion valve to maintain a higher evaporator superheat.
Correct Answer: B - Decrease the gas cooler pressure to 90 bar to
reduce compressor work.
RATIONALE
In transcritical CO2 systems, lowering gas cooler pressure reduces
compressor work and improves efficiency when ambient temperature
is moderate. Increasing pressure would raise energy use. Parallel
compression helps at high ambient, but here pressure reduction is
more direct. Higher superheat reduces capacity.
Question 5
A technician is troubleshooting a refrigeration system with a thermostatic
expansion valve (TXV) that is hunting. Which condition is least likely to cause
this?
A. An oversized TXV relative to the evaporator load.
B. A partially restricted liquid line filter drier.
C. A superheat setting that is too low.
D. A faulty evaporator pressure regulator (EPR) valve.
Correct Answer: D - A faulty evaporator pressure regulator
(EPR) valve.
Page 4
