NATE HEAT PUMP SERVICE EXAM PRACTICE QUESTIONS
AND CORRECT ANSWERS (VERIFIED ANSWERS) PLUS
RATIONALE Q&A INSTANT DOWNLOAD PDF
120 QUESTIONS
TABLE OF CONTENTS
# TOPIC
1 Analyze heat pump performance using pressure-enthalpy diagrams and superheat/subcooling
measurements
2 Diagnose electrical and mechanical faults through systematic troubleshooting and schematic
interpretation
3 Evaluate defrost control strategies and their impact on system efficiency and reliability
4 Apply current regulations and refrigerant handling standards to service procedures
5 Integrate knowledge of system components and controls to optimize heat pump operation in heating and
cooling modes
6 NATE Heat Pump Service Exam Practice Questions And Correct Answers
7 Verified Answers
8 Plus Rationale Q&A Instant Download Pdf
9 Foundations of Heating, Ventilation, Air Conditioning, and Refrigeration (HVAC-R) - Heat Pump Service
10 Applied Heating, Ventilation, Air Conditioning, and Refrigeration (HVAC-R) - Heat Pump Service
11 Advanced Heating, Ventilation, Air Conditioning, and Refrigeration (HVAC-R) - Heat Pump Service
12 Heating, Ventilation, Air Conditioning, and Refrigeration (HVAC-R) - Heat Pump Service Review
Page 1
,Q1 ANALYZE HEAT PUMP PERFORMANCE USING PRESSURE-ENTHALPY DIAGRAMS AND
SUPERHEAT/SUBCOOLING MEASUREMENTS
During heating mode, a heat pump with a fixed orifice metering device is found to
have a subcooling of 5°F and a suction superheat of 50°F. The indoor air
temperature split across the evaporator (indoor coil) is only 10°F. Which of the
following is the most likely cause?
A. Restricted liquid line filter-drier CORRECT
B. Low indoor airflow due to dirty filter
C. Overcharged system
D. Faulty reversing valve
RATIONALE: A restricted liquid line reduces refrigerant flow, causing low subcooling (little liquid
in condenser) and high superheat (starvation of evaporator). Low airflow would cause low
superheat, not high. Overcharge would raise subcooling. A faulty reversing valve would typically
cause pressure equalization or no heating at all.
Q2 ANALYZE HEAT PUMP PERFORMANCE USING PRESSURE-ENTHALPY DIAGRAMS AND
SUPERHEAT/SUBCOOLING MEASUREMENTS
A heat pump in cooling mode has a suction pressure of 68 psig (R-410A) and a
liquid line pressure of 380 psig. The liquid line temperature at the service valve is
100°F. The outdoor ambient is 95°F. What is the most likely cause of the 5°F
subcooling?
A. Low charge CORRECT
B. Dirty outdoor coil
C. Bad TXV sensing bulb
D. Overcharge
RATIONALE: Saturated condensing temperature for R-410A at 380 psig is approximately 105°F,
so subcooling = 105 - 100 = 5°F, which is low. Low charge reduces liquid in the condenser,
lowering subcooling. Dirty coil would raise head pressure and subcooling. TXV issues affect
superheat more. Overcharge would raise subcooling.
Page 2
,Q3 ANALYZE HEAT PUMP PERFORMANCE USING PRESSURE-ENTHALPY DIAGRAMS AND
SUPERHEAT/SUBCOOLING MEASUREMENTS
A heat pump with a dual-fuel system (heat pump + gas furnace) is operating in
heating mode. The outdoor thermostat is set to lock out the heat pump at 35°F.
The system is equipped with an outdoor ambient sensor. Which of the following
conditions would cause the heat pump to continue running below the lockout
temperature?
A. Faulty outdoor ambient sensor reading 10°F higher than actual CORRECT
B. Faulty outdoor ambient sensor reading 10°F lower than actual
C. Stuck auxiliary heat relay
D. Thermostat setpoint too low
RATIONALE: If the sensor reads higher than actual, the control thinks it's warmer than it is, so it
may keep the compressor running below the lockout. A lower reading would lock out earlier.
Stuck relay or low setpoint would not keep the heat pump running.
Q4 ANALYZE HEAT PUMP PERFORMANCE USING PRESSURE-ENTHALPY DIAGRAMS AND
SUPERHEAT/SUBCOOLING MEASUREMENTS
A heat pump's defrost control initiates defrost based on accumulated compressor
run time and coil temperature. During defrost, the outdoor fan is energized, but the
reversing valve does not shift. What is the most likely immediate result?
A. The indoor auxiliary heat will not energize
B. The compressor will overheat and trip on internal overload CORRECT
C. The outdoor coil will melt frost faster due to fan operation
D. The system will continue heating normally
RATIONALE: If the reversing valve fails to shift, the system remains in heating mode while the
outdoor fan runs, causing the outdoor coil to stay cold and frost to accumulate further. The
compressor may overheat due to high compression ratio and lack of cooling. Aux heat is
controlled separately. Fan operation without valve shift does not melt frost.
Page 3
, Q5 ANALYZE HEAT PUMP PERFORMANCE USING PRESSURE-ENTHALPY DIAGRAMS AND
SUPERHEAT/SUBCOOLING MEASUREMENTS
A technician measures the following on an R-410A heat pump in heating mode:
compressor suction pressure 110 psig, discharge pressure 365 psig, suction line
temperature at the compressor 55°F, and liquid line temperature at the TXV inlet
95°F. Outdoor ambient is 40°F, indoor return air is 70°F. What is the most likely
diagnosis?
A. Restricted indoor TXV
B. Low refrigerant charge
C. Faulty check valve in the liquid line
D. Compressor valve leak CORRECT
RATIONALE: Suction pressure corresponds to a saturated temperature of about 45°F (R-410A),
giving superheat of 10°F (55-45). Discharge pressure corresponds to about 100°F, and liquid
temp 95°F gives subcooling of 5°F. These are normal. However, with a compressor valve leak,
the discharge valve leaks back to suction, causing high suction pressure and low discharge
pressure relative to the load. Here, pressures are plausible but not extreme; the key is that
superheat and subcooling are normal, yet the system may be inefficient. Among the options,
compressor valve leak can cause low capacity with normal refrigerant metering. Restricted TXV
would raise superheat. Low charge would raise superheat and lower subcooling. Faulty check
valve would cause pressure drop in heating mode, affecting liquid line pressure but not
necessarily superheat/subcooling.
Page 4
AND CORRECT ANSWERS (VERIFIED ANSWERS) PLUS
RATIONALE Q&A INSTANT DOWNLOAD PDF
120 QUESTIONS
TABLE OF CONTENTS
# TOPIC
1 Analyze heat pump performance using pressure-enthalpy diagrams and superheat/subcooling
measurements
2 Diagnose electrical and mechanical faults through systematic troubleshooting and schematic
interpretation
3 Evaluate defrost control strategies and their impact on system efficiency and reliability
4 Apply current regulations and refrigerant handling standards to service procedures
5 Integrate knowledge of system components and controls to optimize heat pump operation in heating and
cooling modes
6 NATE Heat Pump Service Exam Practice Questions And Correct Answers
7 Verified Answers
8 Plus Rationale Q&A Instant Download Pdf
9 Foundations of Heating, Ventilation, Air Conditioning, and Refrigeration (HVAC-R) - Heat Pump Service
10 Applied Heating, Ventilation, Air Conditioning, and Refrigeration (HVAC-R) - Heat Pump Service
11 Advanced Heating, Ventilation, Air Conditioning, and Refrigeration (HVAC-R) - Heat Pump Service
12 Heating, Ventilation, Air Conditioning, and Refrigeration (HVAC-R) - Heat Pump Service Review
Page 1
,Q1 ANALYZE HEAT PUMP PERFORMANCE USING PRESSURE-ENTHALPY DIAGRAMS AND
SUPERHEAT/SUBCOOLING MEASUREMENTS
During heating mode, a heat pump with a fixed orifice metering device is found to
have a subcooling of 5°F and a suction superheat of 50°F. The indoor air
temperature split across the evaporator (indoor coil) is only 10°F. Which of the
following is the most likely cause?
A. Restricted liquid line filter-drier CORRECT
B. Low indoor airflow due to dirty filter
C. Overcharged system
D. Faulty reversing valve
RATIONALE: A restricted liquid line reduces refrigerant flow, causing low subcooling (little liquid
in condenser) and high superheat (starvation of evaporator). Low airflow would cause low
superheat, not high. Overcharge would raise subcooling. A faulty reversing valve would typically
cause pressure equalization or no heating at all.
Q2 ANALYZE HEAT PUMP PERFORMANCE USING PRESSURE-ENTHALPY DIAGRAMS AND
SUPERHEAT/SUBCOOLING MEASUREMENTS
A heat pump in cooling mode has a suction pressure of 68 psig (R-410A) and a
liquid line pressure of 380 psig. The liquid line temperature at the service valve is
100°F. The outdoor ambient is 95°F. What is the most likely cause of the 5°F
subcooling?
A. Low charge CORRECT
B. Dirty outdoor coil
C. Bad TXV sensing bulb
D. Overcharge
RATIONALE: Saturated condensing temperature for R-410A at 380 psig is approximately 105°F,
so subcooling = 105 - 100 = 5°F, which is low. Low charge reduces liquid in the condenser,
lowering subcooling. Dirty coil would raise head pressure and subcooling. TXV issues affect
superheat more. Overcharge would raise subcooling.
Page 2
,Q3 ANALYZE HEAT PUMP PERFORMANCE USING PRESSURE-ENTHALPY DIAGRAMS AND
SUPERHEAT/SUBCOOLING MEASUREMENTS
A heat pump with a dual-fuel system (heat pump + gas furnace) is operating in
heating mode. The outdoor thermostat is set to lock out the heat pump at 35°F.
The system is equipped with an outdoor ambient sensor. Which of the following
conditions would cause the heat pump to continue running below the lockout
temperature?
A. Faulty outdoor ambient sensor reading 10°F higher than actual CORRECT
B. Faulty outdoor ambient sensor reading 10°F lower than actual
C. Stuck auxiliary heat relay
D. Thermostat setpoint too low
RATIONALE: If the sensor reads higher than actual, the control thinks it's warmer than it is, so it
may keep the compressor running below the lockout. A lower reading would lock out earlier.
Stuck relay or low setpoint would not keep the heat pump running.
Q4 ANALYZE HEAT PUMP PERFORMANCE USING PRESSURE-ENTHALPY DIAGRAMS AND
SUPERHEAT/SUBCOOLING MEASUREMENTS
A heat pump's defrost control initiates defrost based on accumulated compressor
run time and coil temperature. During defrost, the outdoor fan is energized, but the
reversing valve does not shift. What is the most likely immediate result?
A. The indoor auxiliary heat will not energize
B. The compressor will overheat and trip on internal overload CORRECT
C. The outdoor coil will melt frost faster due to fan operation
D. The system will continue heating normally
RATIONALE: If the reversing valve fails to shift, the system remains in heating mode while the
outdoor fan runs, causing the outdoor coil to stay cold and frost to accumulate further. The
compressor may overheat due to high compression ratio and lack of cooling. Aux heat is
controlled separately. Fan operation without valve shift does not melt frost.
Page 3
, Q5 ANALYZE HEAT PUMP PERFORMANCE USING PRESSURE-ENTHALPY DIAGRAMS AND
SUPERHEAT/SUBCOOLING MEASUREMENTS
A technician measures the following on an R-410A heat pump in heating mode:
compressor suction pressure 110 psig, discharge pressure 365 psig, suction line
temperature at the compressor 55°F, and liquid line temperature at the TXV inlet
95°F. Outdoor ambient is 40°F, indoor return air is 70°F. What is the most likely
diagnosis?
A. Restricted indoor TXV
B. Low refrigerant charge
C. Faulty check valve in the liquid line
D. Compressor valve leak CORRECT
RATIONALE: Suction pressure corresponds to a saturated temperature of about 45°F (R-410A),
giving superheat of 10°F (55-45). Discharge pressure corresponds to about 100°F, and liquid
temp 95°F gives subcooling of 5°F. These are normal. However, with a compressor valve leak,
the discharge valve leaks back to suction, causing high suction pressure and low discharge
pressure relative to the load. Here, pressures are plausible but not extreme; the key is that
superheat and subcooling are normal, yet the system may be inefficient. Among the options,
compressor valve leak can cause low capacity with normal refrigerant metering. Restricted TXV
would raise superheat. Low charge would raise superheat and lower subcooling. Faulty check
valve would cause pressure drop in heating mode, affecting liquid line pressure but not
necessarily superheat/subcooling.
Page 4
