HVAC Star Practice Exam

These questions are part of the practice quiz. Start practicing

• If you want to replace a defective capacitor but the only replacements you can find do not have enough capacitance, you can increase their capacitance by
• If refrigerant condenses at a temperature of 105 degrees F and the water leaves the condenser at 95 degrees F, the ___________.
• Which statement is true regarding natural gas pressure for typical household service?
• If not properly installed, a hot-gas muffler might trap:
• Which statement correctly describes AFUE and SEER?
• What simple tool is recommended to verify belt-driven pulley alignment?
• When charging a system, which action should not be used to increase cylinder pressure?
• What is a balancing damper and where is it typically found?
• Which statement describes the relationship between condenser saturation temperature and ambient temperature?
• What should you do just before you work on an electrical circuit?
• What is a common, straightforward diagnostic step when diagnosing furnace ignition problems?
• What are typical operating pressures for an R-410A system on the high side and low side under typical ambient conditions?
• Which pressure-sensing device uses a curved tube that tends to straighten as pressure increases to move a dial?
• The economizer might be described as:
• In a vacuum steam heating system, a common cause of vacuum pump burnout is a
• What is the main difference between fixed-orifice and thermostatic expansion valve (TXV) in regulating refrigerant flow?
• Name three common refrigerant leak detection methods.
• Overload relays should be:
• Electrical pressure is measured in which unit?
• Heat flows downhill. This means:
• Safety limit devices are most often wired in which configuration to protect a load?
• Defrost termination is achieved by time, pressure, and temperature. Which of the following is NOT used as a termination method?
• Superheat is defined as the difference between which two temperatures?
• Why does a flame sensor matter in a gas furnace, and what happens if it fails to detect flame?
• The difference between a contactor and a motor starter is
• What physical property primarily drives capillary action in soldering joints?
• What is the name of a single-phase motor in which the starting capacitor remains connected during run?
• What two physical quantities are sensed by typical bellows in HVAC control?
• Refrigerant leaves the compressor through which line?
• Roller bearings are typically used for which motor and load condition?
• After applying lockout/tagout devices, what is the next critical verification step?
• Fuses in motor branch-circuits primarily provide:
• Which bearing type is not typically used in centrifugal pumps?
• What is the typical suction superheat at the evaporator of an air conditioning system?
• Lock-out relays in air conditioning systems are used to:
• What is the role of a condensate pump in a furnace or air conditioner system?
• Which statement best describes the function of a low-ambient control during cold outdoor conditions?
• To reduce pressure to an acetylene regulator, the adjusting screw is turned
• Compare R-410A and R-22 in terms of operating pressures and lubrication requirements.
• A lamp source has a voltage of 110 volts and a current of 0.9 amperes. What is the resistance of the lamp?
• Which statement best describes where condensate pumped from a furnace or air conditioner should be discharged?
• Define CO detectors, their role, and typical placement in a home with gas appliances.
• What is the purpose of lockout/tagout devices in servicing HVAC equipment?
• State Ohm's law and calculate the resistance of a 24 V thermostat coil drawing 0.8 A.
• What is the function of a contactor in an HVAC system?
• In a three-phase system, the voltage imbalance between any two legs may not vary by more than ______.
• Absolute zero is
• If the vent port on a gas regulator is plugged, which occurs?
• When a stuffing box shaft seal on a centrifugal pump leaks excessively, what maintenance action is recommended?
• Which factor is not used to size gas regulators?
• The efficiency of an electric furnace is usually what percent?
• Outdoor reset of hot water temperature for heating gives hottest water during:
• What is a key advantage of scroll compressors over reciprocating compressors in typical HVAC systems?
• A direct drive pump often uses a ____________ that connects the shaft of the pump motor to the shaft of the circulator pump.
• The refrigerant line that carries liquid refrigerant from the condenser to the metering device is called the ______ line.
• Electricity results from the movement of which particles?
• What is the role of a condensate trap and pump in an air conditioning system?
• Which statement correctly compares PSC and ECM motors in HVAC applications?
• In refrigeration calculations, what is the unit typically used to express heat energy?
• What does SEER stand for, and why does a higher SEER value matter?
• In a cooling tower, increasing the bleed rate will typically do what to the concentration of total dissolved solids?
• The amount of heat removed to lower the temperature of 15 lbs of water from 48 degrees F to 39 degrees F is:
• Cavitation can destroy a centrifugal pump and is caused by which condition?
• Which statement best describes the effect of outdoor temperature on heating capacity: as outdoor temperature decreases, heating capacity tends to:
• What is the purpose of a heat exchanger in a furnace or air conditioner?
• To increase the total capacitance of a capacitor bank, connect capacitors
• The rotation of a three-phase motor can be reversed by interchanging
• With belt driven equipment, alignment of the motor and driven equipment pulleys
• Name two types of bearings used in centrifugal pumps.
• What is the rule of thumb for heat rejection of a condenser in BTU per hour?
• AFUE vs SEER: what does AFUE measure, and how does it differ from SEER?
• Roller bearings are normally used with which condition?
• Which unit is primarily used to rate heating and cooling loads in many HVAC systems?
• The evaporator in a refrigeration system is:
• What is the maximum safe amperage draw of the secondary winding of a 60 VA transformer with a 12-volt output?
• On centrifugal pumps, how should you temporarily reduce pump flow?
• Why are suction line filter-driers equipped with gage connections?
• Electricity results from the movement of which particles?
• Which sequence describes the thermostatic expansion valve response as the sensing bulb reacts?
• What test method could be used to leak test a piping system containing ammonia?
• For an electric heat furnace, what size should the flue pipe be?
• How can you identify reverse operation with a scroll compressor?
• Condenser sizing in a system is typically larger than the evaporator by what percent?
• Which reduced voltage starter uses a switching arrangement to connect the windings of three-phase motors in different configurations during startup and normal operation?
• Why should a hermetic motor not be energized or tested with a megger when in a deep vacuum?
• A thermostatic expansion valve can hunt less when used with a ______ charged element.
• Which gauge uses a flattened metal tube that straightens with increasing pressure?
• An in-line ammeter must be connected to the circuit:
• In an evaporative cooling tower, what is the purpose of adjusting the bleed rate?
• Condensers are sized in a system to be what percent larger than the evaporator?
• Subcooling is most accurately described as which of the following?
• Which statement about economizers is true?
• A dual-element fuse provides two protective features: a thermal cutout and a normal fuse link. Which option correctly lists these two features?
• Outline the basic steps to use a digital multimeter to test a furnace control board for voltage.
• Which device is a common refrigerant leak detector?
• Which instrument would you use to determine atmospheric humidity in HVAC maintenance?
• What is an economizer in HVAC, and when is outdoor air during cooling beneficial?
• In absorption systems, Lithium-Bromide is used as:
• In typical HVAC control circuits, what does the W wire represent?
• With a change in temperature, a thermistor will change:
• Two common types of thermal overload relays used today are
• What should be installed at the bottom of a suction line riser when in doubt?
• Capacity control on a helical-rotary (screw) compressor is obtained using:
• How do you perform a refrigerant charge adjustment using subcooling measurements?
• A pressure switch that contains both a high and a low switch is called a:
• Evaporators should never exceed a pressure drop of:
• For a voltage measurement the meter is connected to a circuit:
• What does AFUE stand for in furnace efficiency ratings?
• What are the first four steps of lockout/tagout (LOTO) when servicing HVAC equipment?
• A transformer rated 60 VA with a 12 V secondary provides how many amperes?
• In a direct-drive pump system, what component connects the motor shaft to the circulator pump shaft?
• Which statement best describes the role of enthalpy in HVAC calculations?
• In a two-stage cooling system, what happens when stage 2 is called?
• A dual-element fuse has which components?
• Describe a basic refrigerant leak test using a soap solution.
• Define superheat and subcooling and explain how each is used to troubleshoot refrigerant charge.
• Why is venting important for high-efficiency condensing furnaces, and what codes govern venting?
• In thermostat wiring, what does the O/B wire control?
• The approach temperature for the evaporator is
• In HVAC control systems, a bellows is used in which controllers?
• What is a duct leakage testing method, and what equipment is typically used?
• What is the purpose of a humidistat in a humidity control system, and how is it used?
• Which lubricants are used with R-22 versus R-410A, and why does it matter?
• Which gas must never be used to pressurize or leak test a refrigeration system?
• Why is a condensate trap and pump necessary in some air conditioning installations?
• What is the purpose of a manifold gauge set in HVAC service, and what do the high and low sides represent?
• Suction gas temperature minus saturated suction temperature equals
• During soldering, what mechanism draws solder into the joint?
• The efficiency of an electric furnace is usually what percent?
• In a two-stage cooling system, how does the thermostat indicate stage 2 operation?
• Explain enthalpy and its use on a psychrometric chart.
• AFUE and HSPF are efficiency metrics used for heating equipment. Which statement is accurate?
• In HVAC control circuits, lock-out relays primarily serve to prevent which condition?
• What is the purpose of a pressure switch in an HVAC system?
• Which gas must never be used to pressurize or leak test a refrigeration system?
• In a pump system, a coupling serves which primary function?
• In a closed transition starting method, which statement is true?
• The refrigerant line that connects the condenser to the metering device is the ______ line.
• Which pressure tends to open the thermostatic expansion valve?
• What is the function of a low-ambient control on a heat pump or air conditioner?
• Where is water contained when it is introduced into the end of a chiller?
• In a capacitor-start motor, the start capacitor is larger than the run capacitor. Which option shows the correct statement?
• To reverse the rotation of a three-phase motor, you can
• How is air changes per hour (ACH) calculated for a room?
• Copper-plating of compressor parts is:
• Which of the following is the correct unit for electrical potential difference?
• Which factor is not typically considered when choosing between a gas and electric furnace?
• Why is subcooling used when charging a refrigerant, and what does high or low subcooling indicate?
• Which statement correctly describes PSIG and psia?
• If a refrigerant sight glass shows bubbles, you know:
• In electrical notation, which symbol is typically used to denote voltage?
• Which flame sensing relay technique relies on ionized hot gases conducting electricity in the flame?
• Define CFM and explain how it relates to duct sizing and air distribution.
• What is latent heat, and how does humidity affect the cooling load in an HVAC system?
• Which thermometer is considered the most accurate?
• Distinguish between a split system and a packaged system in terms of components and installation.
• Why is a manual reset device sometimes required on a safety limit circuit?
• In a megger test on a hermetic motor in deep vacuum, which outcome is expected if performed?
• A vacuum breaker is installed between equipment and a steam trap to
• What is the primary function of a refrigeration compressor?
• Which thermometer is considered the most accurate for HVAC temperature measurement?
• When charging refrigerant, which port on the gauge manifold is used to connect the refrigerant cylinder?
• What factors influence the choice between a gas furnace and an electric furnace?
• Which placement is correct for an in-line ammeter in a circuit?
• 8 kW is equivalent to approximately how many Btu per hour?
• What happens to heat when an object is refrigerated?
• How many Btu are there in 8 kW of electrical power?
• Identify a common reason for furnace ignition failure and a simple diagnostic check.
• The power of a lamp rated at 110 V and 0.9 A is approximately:
• The evaporator function is:
• If a system shows low superheat and high subcooling, what does this typically indicate about the refrigerant charge?
• What does CFM stand for and how is it used in duct design?
• Condenser saturation temperature on an air cooled condenser should be higher than the ambient temperature by:
• What is the function of a two-stage thermostat?
• How is the compression ratio of a refrigeration system determined?
• Copper plating of compressor parts indicates issues with what?
• Lithium-Bromide is used in absorption systems as:
• In aligning a flexible coupling, which two planes must be considered?
• In hot-gas bypass control, which component is bypassed?
• When a three-phase motor single-phases, it
• What is the general requirement for combustion air in a natural gas furnace and how is it supplied?
• As compared to across-the-line starters, reduced voltage starters:
• What is the maximum allowable current imbalance rating in a three-phase supply?
• What air distribution system includes both a warm air duct and a cool air duct and uses mixing boxes near the zone to mix the warm and cool air streams and achieve the desired temperature while delivering air at a near constant volume?
• Which statement about heat flow in natural processes is true?
• Which statement about reduced voltage starters is true?
• What is the common cause of back pressure in a condensate return line?
• What is the purpose of a filter-dryer in a refrigeration system, and what happens if it becomes saturated?
• The instrument used for finding humidity levels in the atmosphere is the
• What does a thermostat do in an HVAC system?
• The heating capacity of an air-to-air heat pump changes as outdoor air gets colder. How does it trend?
• In a thermostatic expansion valve, evaporator pressure and spring pressure both tend to close the valve, while bulb pressure tends to open it. Which option correctly states these effects?
• Which combination of planes is correct for aligning a flexible coupling?
• Which material is commonly used for a direct-drive pump coupling?
• What is the purpose of a thermostat anticipator, and how does it affect system cycling?
• Latent heat is energy associated with moisture changes; humidity increases latent load requiring more cooling.
• Explain the difference between PSIG and psia.
• What is the purpose of the seal in a compressor?
• Which of the following correctly lists common refrigerant metering devices and how each controls refrigerant flow?
• Total capacitance for a CSR motor with a 10 microfarad run capacitor and a 110 microfarad start capacitor is:
• In bearing selection for centrifugal pumps, which pair represents common bearing types?
• Direct-drive pump couplings are commonly made from which material?
• What is the typical suction superheat range at the evaporator?
• Explain the function of the reversing valve in a heat pump.
• What are typical signs that cavitation is occurring in a centrifugal pump?
• Star-delta starters switch windings from star to delta during startup to achieve what main benefit?
• Which device is described as having both a high and a low switch in a single unit?
• The average house line pressure for Natural Gas is:
• Define dew point and explain its significance in HVAC.
• How is duct static pressure measured and why is it important?
• Explain the difference between reciprocating and scroll compressors used in HVAC systems, including typical applications and advantages.
• Which device modulates refrigerant flow based on superheat or temperature?
• Which factor is NOT used to size gas regulators?
• In HVAC motor technology, which statement is true about ECM motors compared to PSC motors?
• The device that protects a vacuum pump from creating too low a vacuum is
• Define BTU and how it relates to cooling/heating loads.
• To add refrigerant to the system through the suction service valve, the valve stem must be:
• Which combination of bearing types is commonly used in centrifugal pumps?
• Which statement best describes a brass coupling?
• Which of the following combinations lists bearing types used in centrifugal pumps?
• Which mode of heat transfer heats a hand near a hot stove most quickly?
• On the Fahrenheit scale, absolute zero is approximately
• Defective rigging components and hardware should be
• A faulty steam trap commonly causes what in the condensate return line?
• What is the function of an outdoor air damper in a ventilation strategy?
• The device that is incorporated into a vacuum steam heating system to protect the vacuum pump from creating too low (deep) a vacuum is a
• Which statement about roller bearings is true?
• In a balanced three-phase system, the phase EMFs differ by what angle?
• In a thermostatic expansion valve, which combination of forces closes the valve?
• Which component in a refrigeration system is described as having a controllable damper as part of its function?
• Which statement best describes HSPF?
• The four main components of a refrigeration system are:
• Which pair of bearing types is commonly used in centrifugal pumps?
• Defrost termination can be controlled by which of the following methods?
• When charging a refrigerant system, which port on the gauge manifold is typically used to connect the refrigerant cylinder?
• Atmospheric pressure at sea level is equal to which value?
• If a stuffing box shaft seal is leaking excessively, which action should be performed?
• The condenser approach temperature is the difference between
• In a chiller, the refrigerant boils by ___________.
• What term describes a refrigerant system condition where refrigerant and/or oil are out of place or have the wrong composition?