UA STAR HVACR MASTERY CERTIFICATION EXAM –
QUESTIONS AND ANSWERS | VERIFIED AND WELL
DETAILED ANSWERS PLUS RATIONALES | GUARANTEED
PASS | LATEST EXAM UPDATE | EXAM PREP | STUDY GUIDE
| PRACTICE TEST| DOWNLOAD INSTANT PDF
1. A technician is troubleshooting a refrigeration system with a TXV metering
device. The evaporator outlet temperature is higher than expected, and the
superheat reading is excessive. What is the most likely cause?
A. Overcharged refrigerant system
B. Restricted refrigerant flow through the metering device
C. Excessive condenser airflow
D. Oversized evaporator coil
Correct Answer: B. Restricted refrigerant flow through the metering device
Rationale: A restricted TXV or insufficient refrigerant flow causes the
evaporator to starve, resulting in high superheat. An overcharge typically causes
high subcooling, while condenser airflow problems affect head pressure rather
than directly causing evaporator starvation.
2. Before beginning service work on a commercial HVACR system, what is
the technician’s most important first action?
A. Verify system pressures
B. Remove all access panels
C. Follow proper lockout/tagout procedures
D. Record refrigerant type
Correct Answer: C. Follow proper lockout/tagout procedures
Rationale: Lockout/tagout protects technicians from electrical and mechanical
hazards before servicing equipment. Pressure checks and documentation are
important but occur after ensuring a safe work environment.
,3. A compressor repeatedly trips on thermal overload after operating for
several minutes. Which condition should the technician investigate first?
A. Compressor overheating caused by poor airflow or high operating pressures
B. Low voltage at the thermostat only
C. Incorrect duct insulation thickness
D. Excessive refrigerant subcooling
Correct Answer: A. Compressor overheating caused by poor airflow or high
operating pressures
Rationale: Thermal overload protection activates when compressor temperature
or current draw becomes excessive. Poor airflow, high head pressure, or
mechanical problems are common causes.
4. What is the primary purpose of superheat measurement in a refrigeration
system?
A. Determine condenser efficiency
B. Verify liquid refrigerant enters the compressor
C. Confirm refrigerant vapor leaving the evaporator is properly heated
D. Measure compressor oil level
Correct Answer: C. Confirm refrigerant vapor leaving the evaporator is
properly heated
Rationale: Superheat confirms that refrigerant leaving the evaporator is vapor
and helps protect the compressor from liquid refrigerant damage.
5. A technician measures low suction pressure and low superheat on an
operating air-conditioning system. Which condition is most likely?
A. Undercharged system
B. Restricted airflow across the evaporator
C. Excessive condenser airflow
D. Failed compressor valves only
,Correct Answer: B. Restricted airflow across the evaporator
Rationale: Low airflow reduces heat transfer, causing the evaporator
temperature and suction pressure to drop while potentially creating low
superheat conditions.
6. When brazing copper refrigeration tubing, why should nitrogen be flowed
through the tubing?
A. To increase brazing temperature
B. To prevent internal oxidation and scale formation
C. To increase refrigerant capacity
D. To reduce compressor oil temperature
Correct Answer: B. To prevent internal oxidation and scale formation
Rationale: Nitrogen purging prevents copper oxide formation inside tubing,
which can contaminate refrigeration components and damage compressors.
7. A building owner reports uneven cooling between rooms. The technician
discovers several supply registers have very low airflow. What should be
checked first?
A. Refrigerant type
B. Compressor oil level
C. Air distribution system restrictions
D. Condenser fan rotation
Correct Answer: C. Air distribution system restrictions
Rationale: Uneven airflow is often caused by duct restrictions, dampers, filters,
or distribution problems before refrigeration issues are considered.
8. Which component changes low-pressure refrigerant vapor into high-
pressure vapor?
, A. Condenser
B. Expansion valve
C. Compressor
D. Receiver
Correct Answer: C. Compressor
Rationale: The compressor raises refrigerant pressure and temperature by
compressing low-pressure vapor into high-pressure vapor.
9. A technician finds a dirty condenser coil during preventive maintenance.
What is the expected system effect if the coil remains dirty?
A. Lower head pressure and reduced efficiency
B. Higher head pressure and increased compressor workload
C. Increased evaporator airflow
D. Lower refrigerant temperature at the outlet
Correct Answer: B. Higher head pressure and increased compressor
workload
Rationale: Dirt restricts heat rejection, causing higher condensing pressures and
forcing the compressor to work harder.
10. Which instrument is commonly used to measure electrical current without
disconnecting conductors?
A. Manifold gauge set
B. Clamp meter
C. Micrometer
D. Psychrometer
Correct Answer: B. Clamp meter
Rationale: A clamp meter measures current by clamping around a conductor,
allowing safe electrical testing without opening the circuit.
QUESTIONS AND ANSWERS | VERIFIED AND WELL
DETAILED ANSWERS PLUS RATIONALES | GUARANTEED
PASS | LATEST EXAM UPDATE | EXAM PREP | STUDY GUIDE
| PRACTICE TEST| DOWNLOAD INSTANT PDF
1. A technician is troubleshooting a refrigeration system with a TXV metering
device. The evaporator outlet temperature is higher than expected, and the
superheat reading is excessive. What is the most likely cause?
A. Overcharged refrigerant system
B. Restricted refrigerant flow through the metering device
C. Excessive condenser airflow
D. Oversized evaporator coil
Correct Answer: B. Restricted refrigerant flow through the metering device
Rationale: A restricted TXV or insufficient refrigerant flow causes the
evaporator to starve, resulting in high superheat. An overcharge typically causes
high subcooling, while condenser airflow problems affect head pressure rather
than directly causing evaporator starvation.
2. Before beginning service work on a commercial HVACR system, what is
the technician’s most important first action?
A. Verify system pressures
B. Remove all access panels
C. Follow proper lockout/tagout procedures
D. Record refrigerant type
Correct Answer: C. Follow proper lockout/tagout procedures
Rationale: Lockout/tagout protects technicians from electrical and mechanical
hazards before servicing equipment. Pressure checks and documentation are
important but occur after ensuring a safe work environment.
,3. A compressor repeatedly trips on thermal overload after operating for
several minutes. Which condition should the technician investigate first?
A. Compressor overheating caused by poor airflow or high operating pressures
B. Low voltage at the thermostat only
C. Incorrect duct insulation thickness
D. Excessive refrigerant subcooling
Correct Answer: A. Compressor overheating caused by poor airflow or high
operating pressures
Rationale: Thermal overload protection activates when compressor temperature
or current draw becomes excessive. Poor airflow, high head pressure, or
mechanical problems are common causes.
4. What is the primary purpose of superheat measurement in a refrigeration
system?
A. Determine condenser efficiency
B. Verify liquid refrigerant enters the compressor
C. Confirm refrigerant vapor leaving the evaporator is properly heated
D. Measure compressor oil level
Correct Answer: C. Confirm refrigerant vapor leaving the evaporator is
properly heated
Rationale: Superheat confirms that refrigerant leaving the evaporator is vapor
and helps protect the compressor from liquid refrigerant damage.
5. A technician measures low suction pressure and low superheat on an
operating air-conditioning system. Which condition is most likely?
A. Undercharged system
B. Restricted airflow across the evaporator
C. Excessive condenser airflow
D. Failed compressor valves only
,Correct Answer: B. Restricted airflow across the evaporator
Rationale: Low airflow reduces heat transfer, causing the evaporator
temperature and suction pressure to drop while potentially creating low
superheat conditions.
6. When brazing copper refrigeration tubing, why should nitrogen be flowed
through the tubing?
A. To increase brazing temperature
B. To prevent internal oxidation and scale formation
C. To increase refrigerant capacity
D. To reduce compressor oil temperature
Correct Answer: B. To prevent internal oxidation and scale formation
Rationale: Nitrogen purging prevents copper oxide formation inside tubing,
which can contaminate refrigeration components and damage compressors.
7. A building owner reports uneven cooling between rooms. The technician
discovers several supply registers have very low airflow. What should be
checked first?
A. Refrigerant type
B. Compressor oil level
C. Air distribution system restrictions
D. Condenser fan rotation
Correct Answer: C. Air distribution system restrictions
Rationale: Uneven airflow is often caused by duct restrictions, dampers, filters,
or distribution problems before refrigeration issues are considered.
8. Which component changes low-pressure refrigerant vapor into high-
pressure vapor?
, A. Condenser
B. Expansion valve
C. Compressor
D. Receiver
Correct Answer: C. Compressor
Rationale: The compressor raises refrigerant pressure and temperature by
compressing low-pressure vapor into high-pressure vapor.
9. A technician finds a dirty condenser coil during preventive maintenance.
What is the expected system effect if the coil remains dirty?
A. Lower head pressure and reduced efficiency
B. Higher head pressure and increased compressor workload
C. Increased evaporator airflow
D. Lower refrigerant temperature at the outlet
Correct Answer: B. Higher head pressure and increased compressor
workload
Rationale: Dirt restricts heat rejection, causing higher condensing pressures and
forcing the compressor to work harder.
10. Which instrument is commonly used to measure electrical current without
disconnecting conductors?
A. Manifold gauge set
B. Clamp meter
C. Micrometer
D. Psychrometer
Correct Answer: B. Clamp meter
Rationale: A clamp meter measures current by clamping around a conductor,
allowing safe electrical testing without opening the circuit.
