HVAC Troubleshooting Practice Exam 2026 |
System Diagnostics Study Guide with Verified
Questions, Answers & Detailed Rationales
HVAC TROUBLESHOOTING PRACTICE EXAM 2026
System Diagnostics Study Guide with Verified Questions, Answers & Detailed
RATIONALE
This practice exam contains 300 carefully crafted questions designed to sharpen your
diagnostic skills and deepen your understanding of HVAC systems. Work through each
question independently before checking the CORRECT ANSWER and RATIONALE
to maximize retention and exam readiness.
QUESTIONS
Question 1 A technician notices that a split air conditioning system is running but not
cooling. The suction line is warm to the touch. What is the MOST likely cause?
A. Overcharged refrigerant
B. Faulty condenser fan motor
C. Low refrigerant charge
D. Dirty evaporator coil
E. Oversized expansion valve
C. Low refrigerant charge
A warm suction line indicates that the refrigerant is not absorbing adequate heat at the
evaporator, which is a classic sign of a low refrigerant charge. Insufficient refrigerant
reduces heat absorption capacity, leaving the suction line warmer than expected.
Question 2 What does a superheat reading that is too high typically indicate in a
refrigeration system?
A. Overcharged system
B. Flooded evaporator
,C. Restricted liquid line filter-drier
D. Undercharged refrigerant or restricted metering device
E. Faulty condenser fan
D. Undercharged refrigerant or restricted metering device
High superheat means refrigerant is fully vaporized too early in the evaporator and
continues absorbing heat as a gas. This happens when too little refrigerant flows
through the evaporator, caused by low charge or a restricted metering device.
Question 3 A heat pump is operating in heating mode. The outdoor coil is completely
frosted over and the unit is not defrosting. What is the MOST likely cause?
A. Low refrigerant charge
B. Defective defrost control board or sensor
C. Dirty air filter
D. Oversized refrigerant charge
E. Blocked indoor coil
B. Defective defrost control board or sensor
When a heat pump fails to initiate defrost, the most common cause is a faulty defrost
control board or a defective temperature or pressure sensor that signals the board to
start the defrost cycle. Without defrost, frost builds up until the outdoor coil is completely
blocked.
Question 4 Which refrigerant is classified as an A2L refrigerant?
A. R-22
B. R-410A
C. R-32
D. R-134a
E. R-404A
, C. R-32
R-32 is classified as an A2L refrigerant — mildly flammable with low toxicity. The A2L
classification indicates low flammability, meaning it requires an ignition source and does
not propagate flame easily. R-22 and R-134a are A1 (non-flammable), while R-410A is
also A1.
Question 5 A technician measures a subcooling value of 3°F on a TXV system. What
does this indicate?
A. System is overcharged
B. System is operating normally
C. System is slightly undercharged
D. Evaporator is flooded
E. Condenser is oversized
C. System is slightly undercharged
Normal subcooling on a TXV system ranges from 10°F to 18°F. A subcooling reading of
3°F is too low, indicating insufficient refrigerant in the condenser to adequately subcool
the liquid line. This points to a low refrigerant charge.
Question 6 What instrument is used to measure the temperature difference across an
evaporator coil?
A. Manometer
B. Megohmmeter
C. Digital psychrometer or thermometer
D. Anemometer
E. Clamp meter
C. Digital psychrometer or thermometer
, A digital thermometer or psychrometer measures dry-bulb temperatures at the supply
and return air sides of the evaporator coil. The temperature difference (delta T) helps
determine if the system is transferring heat properly across the coil.
Question 7 Which of the following is the PRIMARY purpose of a filter-drier in a
refrigeration system?
A. Regulate refrigerant flow
B. Remove moisture and contaminants from the refrigerant
C. Separate liquid and vapor refrigerant
D. Reduce system vibration
E. Increase subcooling
B. Remove moisture and contaminants from the refrigerant
A filter-drier contains desiccant material that absorbs moisture and traps particulates
from the refrigerant circuit. Moisture in a refrigerant system can cause acid formation,
freeze at the metering device, and damage compressor components.
Question 8 A gas furnace ignites but the burner shuts off after a few seconds. What is
the MOST likely cause?
A. Faulty pressure switch
B. Defective flame sensor
C. Cracked heat exchanger
D. Blocked flue pipe
E. Low gas pressure
B. Defective flame sensor
A flame sensor detects the presence of a burner flame by conducting a small microamp
current through the flame. If the sensor is dirty or defective, it fails to confirm the flame
is present, causing the control board to shut off the gas valve as a safety measure
within seconds of ignition.
System Diagnostics Study Guide with Verified
Questions, Answers & Detailed Rationales
HVAC TROUBLESHOOTING PRACTICE EXAM 2026
System Diagnostics Study Guide with Verified Questions, Answers & Detailed
RATIONALE
This practice exam contains 300 carefully crafted questions designed to sharpen your
diagnostic skills and deepen your understanding of HVAC systems. Work through each
question independently before checking the CORRECT ANSWER and RATIONALE
to maximize retention and exam readiness.
QUESTIONS
Question 1 A technician notices that a split air conditioning system is running but not
cooling. The suction line is warm to the touch. What is the MOST likely cause?
A. Overcharged refrigerant
B. Faulty condenser fan motor
C. Low refrigerant charge
D. Dirty evaporator coil
E. Oversized expansion valve
C. Low refrigerant charge
A warm suction line indicates that the refrigerant is not absorbing adequate heat at the
evaporator, which is a classic sign of a low refrigerant charge. Insufficient refrigerant
reduces heat absorption capacity, leaving the suction line warmer than expected.
Question 2 What does a superheat reading that is too high typically indicate in a
refrigeration system?
A. Overcharged system
B. Flooded evaporator
,C. Restricted liquid line filter-drier
D. Undercharged refrigerant or restricted metering device
E. Faulty condenser fan
D. Undercharged refrigerant or restricted metering device
High superheat means refrigerant is fully vaporized too early in the evaporator and
continues absorbing heat as a gas. This happens when too little refrigerant flows
through the evaporator, caused by low charge or a restricted metering device.
Question 3 A heat pump is operating in heating mode. The outdoor coil is completely
frosted over and the unit is not defrosting. What is the MOST likely cause?
A. Low refrigerant charge
B. Defective defrost control board or sensor
C. Dirty air filter
D. Oversized refrigerant charge
E. Blocked indoor coil
B. Defective defrost control board or sensor
When a heat pump fails to initiate defrost, the most common cause is a faulty defrost
control board or a defective temperature or pressure sensor that signals the board to
start the defrost cycle. Without defrost, frost builds up until the outdoor coil is completely
blocked.
Question 4 Which refrigerant is classified as an A2L refrigerant?
A. R-22
B. R-410A
C. R-32
D. R-134a
E. R-404A
, C. R-32
R-32 is classified as an A2L refrigerant — mildly flammable with low toxicity. The A2L
classification indicates low flammability, meaning it requires an ignition source and does
not propagate flame easily. R-22 and R-134a are A1 (non-flammable), while R-410A is
also A1.
Question 5 A technician measures a subcooling value of 3°F on a TXV system. What
does this indicate?
A. System is overcharged
B. System is operating normally
C. System is slightly undercharged
D. Evaporator is flooded
E. Condenser is oversized
C. System is slightly undercharged
Normal subcooling on a TXV system ranges from 10°F to 18°F. A subcooling reading of
3°F is too low, indicating insufficient refrigerant in the condenser to adequately subcool
the liquid line. This points to a low refrigerant charge.
Question 6 What instrument is used to measure the temperature difference across an
evaporator coil?
A. Manometer
B. Megohmmeter
C. Digital psychrometer or thermometer
D. Anemometer
E. Clamp meter
C. Digital psychrometer or thermometer
, A digital thermometer or psychrometer measures dry-bulb temperatures at the supply
and return air sides of the evaporator coil. The temperature difference (delta T) helps
determine if the system is transferring heat properly across the coil.
Question 7 Which of the following is the PRIMARY purpose of a filter-drier in a
refrigeration system?
A. Regulate refrigerant flow
B. Remove moisture and contaminants from the refrigerant
C. Separate liquid and vapor refrigerant
D. Reduce system vibration
E. Increase subcooling
B. Remove moisture and contaminants from the refrigerant
A filter-drier contains desiccant material that absorbs moisture and traps particulates
from the refrigerant circuit. Moisture in a refrigerant system can cause acid formation,
freeze at the metering device, and damage compressor components.
Question 8 A gas furnace ignites but the burner shuts off after a few seconds. What is
the MOST likely cause?
A. Faulty pressure switch
B. Defective flame sensor
C. Cracked heat exchanger
D. Blocked flue pipe
E. Low gas pressure
B. Defective flame sensor
A flame sensor detects the presence of a burner flame by conducting a small microamp
current through the flame. If the sensor is dirty or defective, it fails to confirm the flame
is present, causing the control board to shut off the gas valve as a safety measure
within seconds of ignition.
