CO HVAC Controls Contractor Exam
Practice Questions And Correct
Answers (Verified Answers) Plus
Rationale 2027 Q&A| Instant
Download Pdf.
1. Which control strategy is most appropriate for maintaining a
constant discharge-air temperature from an HVAC air-handling unit
when the heating and cooling loads vary continuously?
A. Two-position control
B. Floating control
C. Proportional-integral control
D. Manual control
Proportional-integral control continuously modulates the controlled
device and corrects both present error and accumulated offset, making
it well suited to maintaining a stable discharge-air temperature under
changing loads.
2. In a variable-air-volume (VAV) HVAC system, what is the primary
purpose of a zone temperature sensor?
A. Measure duct static pressure
B. Detect filter loading
,C. Measure outdoor-air humidity
D. Provide zone temperature feedback to the controller
The zone temperature sensor supplies feedback that allows the
controller to compare actual room temperature with the desired
setpoint and adjust the VAV terminal accordingly.
3. What is the principal function of a differential-pressure sensor
installed across an HVAC filter?
A. Control supply-air temperature
B. Measure refrigerant pressure
C. Detect increasing pressure drop caused by filter loading
D. Control outdoor-air humidity
As a filter becomes loaded with dirt, airflow resistance increases and the
pressure difference across the filter rises, allowing the controls system to
identify a dirty-filter condition.
4. A VAV terminal is equipped with a modulating damper actuator.
Which control signal is commonly used to command the actuator
position?
A. 24 VAC only
B. 0–10 VDC
C. 120 VAC only
D. Dry-contact pulse only
,A 0–10 VDC signal is a common analog control signal in building
automation systems and can represent a proportional damper position
from minimum to maximum.
5. What is the purpose of an actuator's spring-return feature on a
normally closed outside-air damper?
A. Increase airflow during normal operation
B. Reduce actuator power consumption to zero
C. Return the damper to its defined safe position when power is lost
D. Maintain the last commanded position indefinitely
A spring-return actuator uses stored mechanical energy to drive the
damper to its designated fail position when electrical power or the
control signal is removed.
6. In HVAC controls, what does the term "fail-safe position" describe?
A. The position producing maximum airflow under all conditions
B. The position selected by the manufacturer for normal operation
C. The position a controlled device assumes during a defined failure
condition
D. The position required only during commissioning
A fail-safe position is the predetermined state of a damper, valve, or
other device during conditions such as loss of power, loss of signal, or
controller failure.
7. What is the primary purpose of a mixed-air temperature sensor in
an air-handling unit?
, A. Measure chilled-water pressure
B. Measure compressor discharge pressure
C. Monitor the temperature of air after outdoor and return air have
mixed
D. Determine fan bearing temperature
The mixed-air sensor provides feedback about the combined outdoor
and return air stream, which is useful for economizer and freeze-
protection control.
8. An economizer is enabled when outdoor-air conditions are
favorable. What is its primary HVAC control objective?
A. Increase mechanical refrigeration regardless of outdoor conditions
B. Eliminate all return air
C. Use suitable outdoor air to provide cooling and reduce mechanical
cooling demand
D. Maintain maximum outdoor-air intake at all times
An economizer takes advantage of favorable outdoor conditions to
provide free or reduced-cost cooling, thereby lowering mechanical
refrigeration requirements.
9. What condition commonly causes an HVAC controller to command a
chilled-water valve toward a more open position?
A. Supply-air temperature is below setpoint
B. Space temperature is below heating setpoint
C. Cooling demand causes the controlled temperature to rise above its
Practice Questions And Correct
Answers (Verified Answers) Plus
Rationale 2027 Q&A| Instant
Download Pdf.
1. Which control strategy is most appropriate for maintaining a
constant discharge-air temperature from an HVAC air-handling unit
when the heating and cooling loads vary continuously?
A. Two-position control
B. Floating control
C. Proportional-integral control
D. Manual control
Proportional-integral control continuously modulates the controlled
device and corrects both present error and accumulated offset, making
it well suited to maintaining a stable discharge-air temperature under
changing loads.
2. In a variable-air-volume (VAV) HVAC system, what is the primary
purpose of a zone temperature sensor?
A. Measure duct static pressure
B. Detect filter loading
,C. Measure outdoor-air humidity
D. Provide zone temperature feedback to the controller
The zone temperature sensor supplies feedback that allows the
controller to compare actual room temperature with the desired
setpoint and adjust the VAV terminal accordingly.
3. What is the principal function of a differential-pressure sensor
installed across an HVAC filter?
A. Control supply-air temperature
B. Measure refrigerant pressure
C. Detect increasing pressure drop caused by filter loading
D. Control outdoor-air humidity
As a filter becomes loaded with dirt, airflow resistance increases and the
pressure difference across the filter rises, allowing the controls system to
identify a dirty-filter condition.
4. A VAV terminal is equipped with a modulating damper actuator.
Which control signal is commonly used to command the actuator
position?
A. 24 VAC only
B. 0–10 VDC
C. 120 VAC only
D. Dry-contact pulse only
,A 0–10 VDC signal is a common analog control signal in building
automation systems and can represent a proportional damper position
from minimum to maximum.
5. What is the purpose of an actuator's spring-return feature on a
normally closed outside-air damper?
A. Increase airflow during normal operation
B. Reduce actuator power consumption to zero
C. Return the damper to its defined safe position when power is lost
D. Maintain the last commanded position indefinitely
A spring-return actuator uses stored mechanical energy to drive the
damper to its designated fail position when electrical power or the
control signal is removed.
6. In HVAC controls, what does the term "fail-safe position" describe?
A. The position producing maximum airflow under all conditions
B. The position selected by the manufacturer for normal operation
C. The position a controlled device assumes during a defined failure
condition
D. The position required only during commissioning
A fail-safe position is the predetermined state of a damper, valve, or
other device during conditions such as loss of power, loss of signal, or
controller failure.
7. What is the primary purpose of a mixed-air temperature sensor in
an air-handling unit?
, A. Measure chilled-water pressure
B. Measure compressor discharge pressure
C. Monitor the temperature of air after outdoor and return air have
mixed
D. Determine fan bearing temperature
The mixed-air sensor provides feedback about the combined outdoor
and return air stream, which is useful for economizer and freeze-
protection control.
8. An economizer is enabled when outdoor-air conditions are
favorable. What is its primary HVAC control objective?
A. Increase mechanical refrigeration regardless of outdoor conditions
B. Eliminate all return air
C. Use suitable outdoor air to provide cooling and reduce mechanical
cooling demand
D. Maintain maximum outdoor-air intake at all times
An economizer takes advantage of favorable outdoor conditions to
provide free or reduced-cost cooling, thereby lowering mechanical
refrigeration requirements.
9. What condition commonly causes an HVAC controller to command a
chilled-water valve toward a more open position?
A. Supply-air temperature is below setpoint
B. Space temperature is below heating setpoint
C. Cooling demand causes the controlled temperature to rise above its
