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HVAC NEC 2023

HVAC Air Conditioning Practice Test 4

Free HVAC Air Conditioning Practice Test 4. 25 questions covering heat flow from hot to cold, sensible heat measurement with thermometers, dew point temperature, human heat production rates, most common gas compression methods, condenser water temperature differential, BHP and AHP relationship, low velocity and friction losses, series fan configurations, sensible heat removal effects, air distribution strategies, HVAC maintenance intervals, dehumidifier selection, refrigerant cylinder safety, and hydronic heating basics.

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HVAC electrical exams cover electrical theory (Ohm's Law, circuits), transformers, single-phase and three-phase motors, control wiring, safety, and troubleshooting.

Requirements vary by state. HVAC technicians typically need EPA 608 certification and may need a separate electrical license for line voltage work.

Key concepts: Heat always flows from higher temperature to lower temperature (second law of thermodynamics). The BHP (brake horsepower) of a fan is always greater than the AHP (air horsepower) because fan efficiency is less than 100% — the motor must supply more power than what actually goes into the air. At lower duct velocities, friction losses are significantly reduced, making low-velocity designs more energy efficient but requiring larger duct sizes.

25

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45 min

Time

70%

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HVAC Air Conditioning Practice Test 4 — Question List

Question 1: Heat always flows

Upward
Horizontally
Hot to cold
Cold to hot

Question 2: The amount of heat in the air that can be measured by thermometer is called as ……..

Latent heat
Sensible heat
Dew heat
Heat capacity

Question 3: The saturation temperature of any given quantity of water vapor at atmospheric pressure is called as ………..

Dew point
Boiling point
Freezing point
Melting point

Question 4: What is the general cooling estimation usually given for a person?

200 Btu
150 Btu
250 Btu
100 Btu

Question 5: Most air conditioning equipment uses ……………… type of cooling methods in houses and small scale commercial buildings.

Evaporative cooling
Gas compression refrigeration
Cooling with steam
Cold water coil cooling

Question 6: The discharge water is approximately ………………. warmer than supply water in cold-water cooling method.

10<sup>0</sup> F to 15<sup>0</sup>F
35<sup>0</sup> F to 55<sup>0</sup>F
5<sup>0</sup> F to 10<sup>0</sup>F
2<sup>0</sup> F to 15<sup>0</sup>F

Question 7: The brake horse power of an electric motor always higher number than air horsepower

True
False

Question 8: What should be air velocity in the air ducts to minimize the effect of frictional losses?

High
Low
Moderate

Question 9: When two fans are operating in series the CFM of the system is …………..

Same
Doubled
Triple
Quadruple

Question 10: Which of the following can be removed to lower the air temperature?

Latent heat
Sensible heat
Super heat
Dew heat

Question 11: What is "air stratification" in a tall space and what HVAC strategy reduces it?

Air stratification is beneficial because it keeps cool air near the floor where occupants are
Stratification wastes energy by concentrating heated air at the ceiling; destratification strategies include ceiling fans, HVLS fans, and displacement ventilation to mix the air layers
Stratification only occurs in cooling mode — heating mode does not create temperature layering
Stratification is prevented by installing more supply diffusers regardless of their position

Question 12: What is the typical preventive maintenance schedule for a commercial packaged rooftop unit and what are the most critical items?

Commercial RTUs only need maintenance when a fault code appears — preventive maintenance is not necessary
Commercial RTUs need quarterly filter checks, annual coil cleaning, refrigerant charge verification each cooling season, electrical connection torque checks, and belt/bearing inspection
All commercial HVAC maintenance must be done by factory-authorized technicians only — no outside service is permitted
Only the refrigerant level needs annual checking — all other components are maintenance-free for 10 years

Question 13: How is a portable or standalone dehumidifier sized for a space, and how does it work?

Dehumidifiers are selected based only on the cubic footage of the space — humidity level does not matter
Dehumidifiers are sized in pints per day based on room size and starting humidity level; they use a refrigerant cycle to condense moisture but reheat air with the condenser inside — reducing humidity without net cooling
Dehumidifiers cool and dehumidify simultaneously — they are essentially the same as window air conditioners
Portable dehumidifiers do not work in basements because low temperatures prevent moisture condensation

Question 14: According to DOT regulations, what percentage full may a recovery cylinder be filled with refrigerant?

Recovery cylinders may be filled to 100% capacity as long as the ambient temperature is below 75°F
DOT regulations limit refrigerant recovery cylinders to 80% of water capacity by weight — the 20% vapor space prevents over-pressurization if the cylinder warms up
Recovery cylinders may only be filled to 50% capacity because refrigerants expand to twice their liquid volume
There is no fill limit for recovery cylinders — only shipping cylinders have fill restrictions

Question 15: What is a hydronic heating system and how does it differ from a forced-air heating system?

A hydronic system uses electricity to directly heat baseboard convectors without any water or boiler
A hydronic system circulates hot water from a boiler through pipes to terminal units; it offers superior comfort, quiet operation, and zoning compared to forced-air systems but requires a separate system for cooling
Hydronic systems are only used for cooling — a separate steam system is required for heating
Hydronic systems are identical to steam systems — both distribute steam through the same piping

Question 16: How does an enthalpy recovery wheel (total energy wheel) work in an air handling unit and what efficiency can it achieve?

An enthalpy wheel only transfers heat — it does not affect moisture levels between exhaust and supply air
An enthalpy wheel rotates between exhaust and supply airstreams, transferring both heat and moisture with 70-85% total effectiveness — reducing both cooling and dehumidification loads significantly
Enthalpy wheels are only used in industrial applications — they cannot be installed in commercial AHUs
An enthalpy wheel completely replaces mechanical cooling in mild climates

Question 17: What is ice thermal storage and how does it help reduce peak demand charges for commercial building owners?

Ice thermal storage uses ice to cool water for domestic use — it is a water treatment system, not HVAC
Ice thermal storage freezes water at night using off-peak electricity, then melts ice during peak hours to provide cooling — shifting electrical load and reducing demand charges
Ice thermal storage is used to freeze and store refrigerant during the heating season for use in summer
Ice thermal storage systems always increase energy consumption because freezing water requires more energy than cooling water

Question 18: What is a Building Automation System (BAS) and what functions does it perform for HVAC control?

A BAS is a fire alarm system that also monitors HVAC temperature setpoints
A BAS is a networked control system managing HVAC scheduling, equipment sequencing, alarm management, optimal start/stop, demand limiting, energy reporting, and fault detection across a building
A BAS only controls lighting — HVAC equipment has separate dedicated controllers that cannot be networked
BAS systems are only used in buildings over 100,000 sq ft — smaller buildings use standalone thermostats

Question 19: What are the two main types of refrigerant recovery machines and what are the advantages of each?

The two types of recovery machines are high-pressure and low-pressure, used for R-410A and R-22 respectively
Vapor recovery machines pull refrigerant as vapor (slower but can achieve low final pressures); liquid recovery machines recover liquid directly at 10-50 lbs/min (much faster for large systems)
There is only one type of recovery machine — all refrigerants are recovered using the same process
Recovery machine type is selected based on refrigerant GWP, not on the type of refrigerant (vapor/liquid)

Question 20: What is AFUE and what distinguishes an 80 AFUE from a 96 AFUE gas furnace?

AFUE only measures how fast a furnace heats — a higher number means faster heat delivery
AFUE measures what percentage of fuel becomes useful heat; a 96 AFUE condensing furnace extracts latent heat from exhaust vapors using a second heat exchanger, venting through PVC at 120°F instead of metal flue at 500°F
80 AFUE and 96 AFUE furnaces use the same combustion process — only the thermostat differs
96 AFUE furnaces waste more fuel but heat faster — the AFUE number indicates speed, not efficiency

Question 21: A customer calls saying their AC runs all the time but produces very little cooling. A technician arrives and finds ice on the indoor coil. What is the correct diagnostic and repair sequence?

Add refrigerant immediately because icing always means the system is undercharged
First thaw the coil completely (fan only, compressor off), then diagnose: check airflow (filter, blower, static pressure), then refrigerant charge — do not add refrigerant until the coil is thawed and cause identified
Ice on the coil is normal in summer — restart the system and the ice will thaw on its own during the next cycle
Replace the indoor coil immediately because icing always indicates a coil that has failed

Question 22: What information can be decoded from the ASHRAE refrigerant numbering system for HFC refrigerants?

Refrigerant numbers are arbitrary — they have no relationship to molecular structure
The ASHRAE number encodes molecular structure: digit positions indicate carbon, hydrogen, and fluorine atom counts; letter suffixes indicate isomers or specific blend compositions
The refrigerant number only indicates the year of development — R-410A was developed in 1941
R-400 series are always single-molecule pure refrigerants, while R-100 series are always blends

Question 23: What fire and smoke control functions must HVAC systems provide in commercial buildings according to building codes?

HVAC systems have no fire safety role — fire suppression is handled entirely by sprinkler systems
Commercial HVAC must include: AHU smoke detector auto-shutdown, fire dampers at fire wall penetrations, smoke dampers for smoke control, stairwell pressurization, and atrium smoke exhaust per IBC and NFPA 90A
Fire dampers and smoke dampers are the same device — they can be used interchangeably
HVAC fire safety requirements only apply to buildings over 10 stories — low-rise commercial is exempt

Question 24: How does a Variable Frequency Drive (VFD) control an HVAC fan motor and what are its main benefits?

VFDs change the motor voltage to control speed — higher voltage means higher speed
VFDs vary the output frequency to control motor speed; fan power follows the cube of speed ratio — reducing speed to 80% saves 49% of power. Benefits include huge energy savings at part load and soft starting
VFDs can only slow fan motors down, not speed them up above normal operation
VFDs reduce energy but increase motor temperature — they require special cooling systems

Question 25: What is "chilled water temperature reset" and how does it improve chiller plant efficiency?

Chilled water temperature reset lowers the chilled water supply temperature to improve humidity removal
Chilled water reset raises the setpoint during lower demand periods; each degree rise saves 1.5-2% chiller energy because higher evaporating temperature means less compression work needed
Chilled water reset only benefits cooling towers — it has no effect on chiller efficiency
Raising chilled water temperature always compromises humidity control and should never be used in humid climates

Key NEC References for This Test

Article	What It Covers
Art. 440	Air Conditioning Equipment — use nameplate MCA and MOCP, not FLA alone
Art. 430	Motors — general motor rules that Art. 440 modifies

Study Tip: Practice reading ladder diagrams. Trace each rung from L1 to the load: contacts open → circuit dead. Contacts closed → current flows. This is how HVAC electrical troubleshooting works.

EXAM CARD HVAC

Questions25

Time limit45 min

Pass score70%

Code editionNEC 2023

DifficultyIntermediate

Last reviewedJun 2026

Timer starts immediately. Progress is auto-saved.

Source: NEC 2026 Art. 440 & electrical theory