HVAC Controls 26408-23 Practice Test

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• In a mechanical refrigeration circuit, what is the purpose of the evaporator?
• What is the purpose of a pressure sensor in a hydronic system?
• Which thermostat terminal is most commonly used to energize the reversing valve in a heat pump?
• Why is regular sensor calibration and maintenance essential for controls?
• What distinguishes commissioning from recommissioning in HVAC controls?
• Which term describes the difference between the heating cycle's turn-on and turn-off temperatures in a thermostat?
• Describe a typical boiler startup sequence.
• Which device delays the furnace blower startup to improve efficiency?
• What is primary/secondary pumping in a chiller plant used for?
• What is night setback and what energy benefit does it provide?
• Differentiate between VAV and CAV systems.
• What is the primary purpose of a damper actuator in a VAV system?
• Name two occupancy sensing technologies used in HVAC controls.
• In a standard thermostat wiring scheme, the R wire originates from the __________.
• A device that generates a voltage proportional to temperature difference is called a
• Which digital control system is designed to serve multiple zones with varying air flow?
• In a chilled water plant startup, when should the chiller compressors be started relative to head pressure?
• What is the primary purpose of the defrost cycle in a heat pump?
• Why do conventional line-voltage thermostats lack precise temperature control?
• Economizer lockout is a control setting that does what?
• Which control strategy explicitly uses outdoor air modulation along with reheat or VAV to meet air-quality and temperature goals?
• What prevents an automatic-changeover thermostat from cycling back and forth between heating and cooling?
• Which thermostat terminal is commonly used for cooling control?
• In a heating system, with the fan switch set to AUTO, which motors run when the thermostat calls for heat?
• The heat anticipator in a heating-only thermostat is a(n) ____________ in series with ____________.
• What is BACnet and why is it important in HVAC controls?
• Permanently installed energy storage systems are covered in NEC in
• Which of the following options lists the four basic refrigerant circuit components used in a cooling/refrigeration system?
• How does demand limiting improve building energy performance?
• Compare pneumatic controls with electronic controls in HVAC systems.
• How do CO2 sensors contribute to IAQ-based ventilation control?
• Why is a deadband typically implemented around the thermostat setpoint?
• In a modern building automation system, which statement best describes the role of a field controller?
• Which principle states that heat is created in one place and carried to another by means of air or water?
• Which scenario typically triggers recommissioning of HVAC controls?
• During a defrost cycle, heat pumps melt ice on the outside coil using which heat source?
• Which device delays the furnace blower startup to increase efficiency?
• What is the role of a damper actuator in a VAV system?
• What are the three basic elements of a control loop?
• What is ASHRAE 62.1 and what does it require for ventilation?
• Which device is connected to the G terminal in a typical thermostat circuit?
• Which NEC article addresses permanently installed energy storage systems?
• In BACnet terms, what is the difference between Analog Input and Binary Input?
• In the described bimetal strip, which metals form the bonded pair?
• The component in an air conditioning or refrigeration system to which the heat from the conditioned space or item being cooled is transferred to the refrigerant is the
• Which statement about thermostat installation height is true?
• A freezestat is best described as which type of switch?
• Trend log data records which of the following?
• In a closed-loop HVAC control, what happens when the sensor detects deviation from the setpoint?
• In an air-to-air heat pump, defrost is accomplished by switching to which mode?
• In the short cycle timer circuit, the yellow wire from the thermostat to the timer is connected to terminal _________.
• Which action helps control condenser head pressure in a cooling system?
• Heat pumps provide heat by ________.
• Which control voltages are commonly used for field devices and why is voltage compatibility important?
• A reset schedule reduces energy consumption by doing what?
• During a fire event, what is a key HVAC control action related to smoke control?
• Which device uses dissimilar metals to control electron flow?
• Which description best matches a VAV with zone sensing control?
• What is the difference between a digital signal and an analog signal?
• What is the purpose of a lockout relay in a comfort cooling control circuit?
• In a heat pump, which thermostat terminal is typically connected to the reversing valve control?
• A defective lockout relay should be replaced with an exact duplicate, sometimes called what?
• Which of the following would be considered a digital device?
• Which refrigerant path carries high-pressure vapor from the compressor to the condenser?
• In a refrigeration cycle, which component absorbs heat from the space being cooled?
• A good location for a thermostat is ________.
• What is the purpose of interlocks in HVAC control systems?
• Why is a minimum damper position important in outdoor air control?
• What is the primary benefit of a two-pump configuration in a chiller plant (primary/secondary pumping)?
• Trend log data is best described as which of the following?
• In the refrigeration cycle, which device raises the pressure of the refrigerant on the high-pressure side?
• What is a deadband in thermostat control?
• The Seebeck effect is the principle behind which device?
• In IAQ-based ventilation, which parameter is commonly used to determine the need for outdoor air?
• Which of the following is NOT one of the four basic refrigerant circuit components?
• The function of a heat sequencer is to _________.
• Older conventional thermostats commonly contain which hazardous material requiring special disposal?
• Conventional line-voltage thermostats are less precise because
• The tubing that carries heat-laden refrigerant gas from the evaporator to the compressor is the
• The recommended installed height for a thermostat is
• What is the purpose of logging events in alarm management within a BAS?
• Which occurs as soon as a heating thermostat is closed?
• Why is there a minimum outdoor air ventilation requirement in HVAC control?
• What is a standard installation height for a thermostat on an interior wall to ensure accurate sensing?
• The R terminal in a standard thermostat wiring scheme is connected to the ______ of the 24V control transformer.
• What is static pressure in a duct system and why is it monitored by controls?
• The rating of cord- and plug-connected room air conditioners must not exceed what percentage of the branch circuit rating when lighting units are also supplied?
• Which statement best describes the metals used in the described bimetal strip?
• Which component stores electrical energy and can retain a charge after power is removed?
• Which of these causes could be immediately eliminated if a compressor is defective?
• Which sequence correctly describes a typical startup sequence for a chilled water plant?
• In a boiler system, what is the heat exchange medium?
• What is the name of the limit switch that senses flame outside the heat exchanger?
• Heat pumps provide heat by reversing the cooling cycle.
• Which NEC article governs motors for refrigeration compressors when using conventional (nonhermetic) motors?
• If a mercury thermostat seems out of adjustment, what is the first step?
• A device that uses dissimilar metals to control electron flow is known as a
• Which practice benefits most from having a clearly defined sequence of operation (SOO)?
• Which device is commonly activated by a thermostat call for heat in many HVAC systems?
• The NEC requirements for fixed electric space-heating equipment are covered in which NEC article?
• What is the main difference between open-loop and closed-loop control in HVAC systems?
• Which device can retain a high-voltage charge after power has been removed?
• How does economizer damper control logic decide when to open or close?
• Which two conditions typical factors in initiation of a defrost cycle in a heat pump?
• Low-voltage (24VAC) control circuits are used in HVAC systems because __________.
• Why does a bimetal strip bend as the temperature changes?
• In the electrical control circuit of a cooling-only system, the outdoor fan motor ________.
• Thermostats with bimetal sensing elements typically use a combination of copper or brass and which alloy?
• Which component primarily modulates zone cooling in a VAV system?
• What is NFPA 90A and how does it relate to HVAC controls?
• In economizer operation, what is the effect when outdoor air conditions are favorable?
• What is the function of an Analog Input in a BACnet-enabled HVAC control?
• The Seebeck effect underlies which type of device?
• What device prevents the compressor from re-starting immediately after shutdown due to pressure build-up?
• In BACnet terms, what is the difference between Analog Output and Binary Output?
• A conventional thermostat should not be thrown into the regular trash because it
• Verifying OA mix during cooling coil troubleshooting ensures what?
• The device that prevents automatic restart after a fault in cooling systems is called a
• What is occupancy-based ventilation and how is it typically implemented?
• What does a "lockout" mean in an HVAC control sequence?
• Which control approach primarily uses microprocessors, sensors, and digital communication to manage HVAC equipment?
• The device that provides the pressure drop that lowers the boiling point of the refrigerant in a refrigerant circuit is the __________.
• Which factors influence condenser head pressure in a cooling system, and how is it controlled?
• Which statement lists the devices typically involved in HVAC safety interlocks?
• The abbreviation FLC in electrical design stands for
• What could be a consequence of not monitoring static pressure in a duct system?
• What is the difference between a 2-position valve and a 3-position valve?
• What is the primary purpose of a Basis of Design (BOD) document in HVAC projects?
• Which statement accurately describes the disconnecting requirement for heating equipment?
• In the mechanical refrigeration cycle, the refrigerant leaving the evaporator is a ________.
• The purpose of a control that monitors the pressure in a gas furnace heat exchanger is to verify what?
• The G terminal would be connected to the _________.
• What is the minimum interlock setting on automatic changeover thermostats commonly called?
• For heat pumps, which characteristic is considered a required feature related to supplemental heat?
• The type of digital control building system designed to serve multiple zones is the ________.
• The provisions for room air conditioners are referenced in ________.
• Which steps are part of a troubleshooting approach if a cooling coil fails to deliver expected cooling?
• In a hydronic heating system, what is the heat transfer medium?
• In a modern building automation system, which statement best describes the field controller's scope?
• What does a three-way valve do in a hydronic heating or cooling circuit?
• Which statement correctly describes why a bimetal thermostat responds to temperature changes?
• How do owner requirements (OPR) and basis of design (BOD) influence control strategies?
• What is a sequence of operation (SOO) and why is it critical in commissioning?
• Which three control strategies are commonly used in zone control for HVAC units such as AHUs, VAVs, or fan-coil units?
• What is the purpose of a high-limit switch?
• Which would be an optional feature for an air conditioning control system?
• Which of the following is an example of an external analog device?
• What is the primary objective of alarm management in a building automation system (BAS)?
• What is the value of setting up trend alerts and alarms in a BAS?
• Multistage thermostats save energy by cycling on heating or cooling stages based on what?
• Which fossil fuel is most widely used?
• How should HVAC controls coordinate with fire and life safety systems?
• Which component stores energy in an electric field and is commonly used in motor control circuits?
• When a typical heat pump is operating in defrost mode, what usually happens indoors?
• In heat pump systems, what feature adds extra heating by design?
• Where should temperature sensors be placed for accurate control and why?
• Which instrument would you use to verify the voltage output of a temperature sensor that generates millivolt-level signals?
• What device uses dissimilar metals to generate a voltage proportional to temperature?
• What device acts as a safety shutoff by responding to temperature changes to prevent equipment overheating in HVAC systems?
• If the compressor motor, OFM, an indoor fan motor (IFM) all fail to operate on a cooling call, the most likely cause __________.
• In the thermostat wiring, which terminal is used for the heating control?
• What component staggers electric heater startup to prevent circuit overload?
• Connecting a 120V heating cable to a 240V circuit will
• According to NEC Section 440.7, the largest motor is considered the one that ________.
• A limit control is a heat-actuated switch positioned above or beside ______.
• The NEC section that specifies the location and accessibility of air conditioning equipment disconnects is
• Which safety device is designed to detect flame rollout and open the circuit if flame is not contained?
• NEC Article 440, Part V covers
• Why is sensor calibration important in HVAC controls?
• If the IFR operates and the fan starts when the thermostat fan switch is set to On, and the relay operates when the switch is set to Auto, the most likely cause is a defective ___________.
• The pressure-based control in a gas furnace heat exchanger is used to verify that which component is operating correctly?
• The purpose of a compressor short-cycle timer is to __________.
• What is the defrost cycle used to prevent in a heat pump's outdoor coil?
• The thermostat terminal normally assigned to cooling control is which?
• A heat anticipator is used in an electromechanical heating thermostat to ______.
• Which statement best describes a freezestat?
• When refrigeration compressors are driven by conventional (nonhermetic) motors, the motors and controls are subject to the requirements in
• What is a disadvantage of a bimetal thermostat when compared to an electronic thermostat?
• The term that describes heat moving from one location to another due to a temperature difference is known as what?
• The key to successful control system is the integration of the ___________ and the _____________
• Which option best describes HVAC safety interlock components?
• When you are installing a 24V thermostat, to which terminals of the thermostat should you connect the 24VAC power supply and what color wires would you use?
• What is a reset schedule in HVAC controls?
• Conductor sizing for multiple hermetic compressors must include total load plus what percentage of the largest motor's full-load current?
• How does a variable frequency drive (VFD) affect energy use in fans and pumps?
• In a standard thermostat wiring scheme, the heating control is wired to terminal
• In a refrigeration system, which component rejects heat from the refrigerant to ambient air?
• When is reheat used in a VAV system?
• Which component is used to filter and store energy in motor circuits, helping reduce voltage spikes?
• Which device can retain a high-voltage charge after power is removed?
• What is setpoint creep and how can it be prevented?
• The differential in an automatic-changeover thermostat is _______.
• Which instrument is used to check the output of a thermocouple?