, Question 1
A technician measures a compressor's suction pressure at 60 psig and discharge
pressure at 250 psig. The ambient temperature is 95°F. If the system uses
R-410A and the evaporator superheat is 12°F, what is the most likely cause of
the high discharge pressure?
A. Overcharged system
B. Restricted liquid line filter drier
C. Inefficient compressor
D. Low evaporator airflow
Correct Answer: A - Overcharged system
RATIONALE
High discharge pressure with normal superheat indicates excess
refrigerant charge, as the condenser cannot subcool adequately. A
restricted filter drier would cause low suction pressure and high
superheat, while low airflow would increase superheat. An inefficient
compressor would reduce both pressures.
Question 2
In a balanced ventilation system, the total external static pressure is measured
at 0.80 in. w.c. The blower performance data shows that at 0.80 in. w.c., the
blower delivers 1200 CFM. If the system requires 1400 CFM, which of the
following modifications is most effective?
A. Increase blower speed to high tap
B. Reduce duct resistance by enlarging return grilles
C. Install a larger evaporator coil
D. Decrease refrigerant charge
Correct Answer: B - Reduce duct resistance by enlarging return
grilles
Page 2
, RATIONALE
Reducing duct resistance lowers external static pressure, allowing the
blower to deliver more airflow. Increasing blower speed may help but
could exceed motor limits. A larger coil affects refrigerant-side
performance, not airflow directly. Refrigerant charge does not affect
airflow.
Question 3
A 3-phase, 460V, 25-ton rooftop unit has a compressor with a rated RLA of
40A. The measured current is 32A on all legs. The condenser entering air
temperature is 85°F, and the leaving air temperature is 105°F. What is the most
likely diagnosis?
A. Compressor is underloaded due to low refrigerant charge
B. Compressor is operating normally
C. Compressor is single-phasing
D. Condenser fan motor is failing
Correct Answer: B - Compressor is operating normally
RATIONALE
A current draw below RLA with a 20°F temperature rise across the
condenser indicates normal operation. Low charge would reduce
current but also lower discharge pressure and temperature rise.
Single-phasing would cause high current on remaining legs. A failing
condenser fan would increase discharge pressure and current.
Question 4
When using the psychrometric chart, the condition of air at 75°F dry-bulb and
50% relative humidity has a dew point closest to which value?
A. 45°F
B. 55°F
C. 65°F
D. 75°F
Page 3
, Correct Answer: B - 55°F
RATIONALE
At 75°F DB and 50% RH, the dew point is approximately 55°F. This
is found by following the horizontal line from the saturation curve at
the intersection of 75°F and 50% RH. Options A, C, and D are
incorrect as they do not align with the psychrometric properties.
Question 5
A refrigeration system using R-134a has a suction pressure of 30 psig and a
head pressure of 150 psig. The evaporator saturation temperature is 35°F, and
the suction line temperature is 50°F. What is the superheat?
A. 5°F
B. 10°F
C. 15°F
D. 20°F
Correct Answer: C - 15°F
RATIONALE
Superheat is the difference between suction line temperature and
evaporator saturation temperature. Using a pressure-temperature chart
for R-134a, 30 psig corresponds to 35°F. Thus, 50°F - 35°F = 15°F
superheat. Other options miscalculate the difference.
Question 6
An ECM blower motor in a variable-speed air handler is drawing high current
and running at full speed continuously. The system is set to 'fan on' and the
thermostat is not calling for cooling. Which component is most likely faulty?
A. Blower motor module
B. Thermostat
C. Control board relay
D. Limit switch
Page 4
A technician measures a compressor's suction pressure at 60 psig and discharge
pressure at 250 psig. The ambient temperature is 95°F. If the system uses
R-410A and the evaporator superheat is 12°F, what is the most likely cause of
the high discharge pressure?
A. Overcharged system
B. Restricted liquid line filter drier
C. Inefficient compressor
D. Low evaporator airflow
Correct Answer: A - Overcharged system
RATIONALE
High discharge pressure with normal superheat indicates excess
refrigerant charge, as the condenser cannot subcool adequately. A
restricted filter drier would cause low suction pressure and high
superheat, while low airflow would increase superheat. An inefficient
compressor would reduce both pressures.
Question 2
In a balanced ventilation system, the total external static pressure is measured
at 0.80 in. w.c. The blower performance data shows that at 0.80 in. w.c., the
blower delivers 1200 CFM. If the system requires 1400 CFM, which of the
following modifications is most effective?
A. Increase blower speed to high tap
B. Reduce duct resistance by enlarging return grilles
C. Install a larger evaporator coil
D. Decrease refrigerant charge
Correct Answer: B - Reduce duct resistance by enlarging return
grilles
Page 2
, RATIONALE
Reducing duct resistance lowers external static pressure, allowing the
blower to deliver more airflow. Increasing blower speed may help but
could exceed motor limits. A larger coil affects refrigerant-side
performance, not airflow directly. Refrigerant charge does not affect
airflow.
Question 3
A 3-phase, 460V, 25-ton rooftop unit has a compressor with a rated RLA of
40A. The measured current is 32A on all legs. The condenser entering air
temperature is 85°F, and the leaving air temperature is 105°F. What is the most
likely diagnosis?
A. Compressor is underloaded due to low refrigerant charge
B. Compressor is operating normally
C. Compressor is single-phasing
D. Condenser fan motor is failing
Correct Answer: B - Compressor is operating normally
RATIONALE
A current draw below RLA with a 20°F temperature rise across the
condenser indicates normal operation. Low charge would reduce
current but also lower discharge pressure and temperature rise.
Single-phasing would cause high current on remaining legs. A failing
condenser fan would increase discharge pressure and current.
Question 4
When using the psychrometric chart, the condition of air at 75°F dry-bulb and
50% relative humidity has a dew point closest to which value?
A. 45°F
B. 55°F
C. 65°F
D. 75°F
Page 3
, Correct Answer: B - 55°F
RATIONALE
At 75°F DB and 50% RH, the dew point is approximately 55°F. This
is found by following the horizontal line from the saturation curve at
the intersection of 75°F and 50% RH. Options A, C, and D are
incorrect as they do not align with the psychrometric properties.
Question 5
A refrigeration system using R-134a has a suction pressure of 30 psig and a
head pressure of 150 psig. The evaporator saturation temperature is 35°F, and
the suction line temperature is 50°F. What is the superheat?
A. 5°F
B. 10°F
C. 15°F
D. 20°F
Correct Answer: C - 15°F
RATIONALE
Superheat is the difference between suction line temperature and
evaporator saturation temperature. Using a pressure-temperature chart
for R-134a, 30 psig corresponds to 35°F. Thus, 50°F - 35°F = 15°F
superheat. Other options miscalculate the difference.
Question 6
An ECM blower motor in a variable-speed air handler is drawing high current
and running at full speed continuously. The system is set to 'fan on' and the
thermostat is not calling for cooling. Which component is most likely faulty?
A. Blower motor module
B. Thermostat
C. Control board relay
D. Limit switch
Page 4
