NC Plumbing, Heating & Fire Sprinkler Contractors
Board – Heating (HVAC) Contractor Examination
(Group 3) Questions and Correct Answers (Verified
Answers) Plus Rationale 2027 Q&A| Instant
Download Pdf
1. What is the primary purpose of a furnace heat exchanger?
A. To increase refrigerant pressure
B. To transfer heat from combustion gases to circulating air
C. To regulate gas supply pressure
D. To remove moisture from indoor air
Answer: B. To transfer heat from combustion gases to circulating air
Rationale: The heat exchanger separates combustion products from
the air delivered to the occupied space while allowing heat to transfer
between them. A cracked or damaged heat exchanger can allow
combustion gases, including carbon monoxide, to enter the supply
airstream.
,2. Which component controls the temperature of a conditioned space
by sensing room temperature?
A. Flame sensor
B. Limit switch
C. Thermostat
D. Pressure switch
Answer: C. Thermostat
Rationale: A thermostat senses indoor temperature and sends a
control signal to the heating or cooling equipment. Depending on the
system, it may initiate heating, cooling, fan operation, or other
functions.
3. What is the purpose of a furnace high-limit switch?
A. To increase blower speed during normal operation
B. To shut down the burner if furnace temperature becomes excessive
C. To increase gas pressure
D. To control outdoor humidity
Answer: B. To shut down the burner if furnace temperature becomes
excessive
,Rationale: The high-limit control protects the furnace from
overheating. Excessive temperature can result from restricted airflow,
an improperly adjusted burner, a dirty filter, blower problems, or
other conditions.
4. A dirty air filter in a forced-air heating system can cause which
condition?
A. Increased airflow
B. Reduced temperature rise
C. Restricted airflow and overheating
D. Increased combustion efficiency
Answer: C. Restricted airflow and overheating
Rationale: A heavily loaded filter increases resistance to airflow.
Reduced airflow can cause the furnace heat exchanger and supply air
temperature to rise excessively, potentially causing the high-limit
control to open.
5. What instrument is commonly used to measure static pressure in
an HVAC duct system?
, A. Manometer
B. Hygrometer
C. Tachometer
D. Thermocouple
Answer: A. Manometer
Rationale: A manometer or digital pressure instrument can measure
positive, negative, and differential pressures in HVAC systems. Static-
pressure measurements are useful for diagnosing airflow restrictions
and duct-system problems.
6. What is the purpose of a furnace flame sensor?
A. To measure room humidity
B. To verify that the burner flame has been established
C. To measure duct static pressure
D. To control blower belt tension
Answer: B. To verify that the burner flame has been established
Rationale: The flame sensor provides the ignition control with
confirmation that combustion is occurring. If flame is not proven
within the required sequence, the control generally shuts off the gas
valve as a safety measure.
Board – Heating (HVAC) Contractor Examination
(Group 3) Questions and Correct Answers (Verified
Answers) Plus Rationale 2027 Q&A| Instant
Download Pdf
1. What is the primary purpose of a furnace heat exchanger?
A. To increase refrigerant pressure
B. To transfer heat from combustion gases to circulating air
C. To regulate gas supply pressure
D. To remove moisture from indoor air
Answer: B. To transfer heat from combustion gases to circulating air
Rationale: The heat exchanger separates combustion products from
the air delivered to the occupied space while allowing heat to transfer
between them. A cracked or damaged heat exchanger can allow
combustion gases, including carbon monoxide, to enter the supply
airstream.
,2. Which component controls the temperature of a conditioned space
by sensing room temperature?
A. Flame sensor
B. Limit switch
C. Thermostat
D. Pressure switch
Answer: C. Thermostat
Rationale: A thermostat senses indoor temperature and sends a
control signal to the heating or cooling equipment. Depending on the
system, it may initiate heating, cooling, fan operation, or other
functions.
3. What is the purpose of a furnace high-limit switch?
A. To increase blower speed during normal operation
B. To shut down the burner if furnace temperature becomes excessive
C. To increase gas pressure
D. To control outdoor humidity
Answer: B. To shut down the burner if furnace temperature becomes
excessive
,Rationale: The high-limit control protects the furnace from
overheating. Excessive temperature can result from restricted airflow,
an improperly adjusted burner, a dirty filter, blower problems, or
other conditions.
4. A dirty air filter in a forced-air heating system can cause which
condition?
A. Increased airflow
B. Reduced temperature rise
C. Restricted airflow and overheating
D. Increased combustion efficiency
Answer: C. Restricted airflow and overheating
Rationale: A heavily loaded filter increases resistance to airflow.
Reduced airflow can cause the furnace heat exchanger and supply air
temperature to rise excessively, potentially causing the high-limit
control to open.
5. What instrument is commonly used to measure static pressure in
an HVAC duct system?
, A. Manometer
B. Hygrometer
C. Tachometer
D. Thermocouple
Answer: A. Manometer
Rationale: A manometer or digital pressure instrument can measure
positive, negative, and differential pressures in HVAC systems. Static-
pressure measurements are useful for diagnosing airflow restrictions
and duct-system problems.
6. What is the purpose of a furnace flame sensor?
A. To measure room humidity
B. To verify that the burner flame has been established
C. To measure duct static pressure
D. To control blower belt tension
Answer: B. To verify that the burner flame has been established
Rationale: The flame sensor provides the ignition control with
confirmation that combustion is occurring. If flame is not proven
within the required sequence, the control generally shuts off the gas
valve as a safety measure.
