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HVAC NEC 2023

HVAC Air Conditioning Practice Test 2

Free HVAC Air Conditioning Practice Test 2. 25 questions covering latent heat and state changes, relative humidity ranges, Boyle's Law, refrigerant vapor compression, occupant ventilation requirements, air cleaning principles, ASHRAE comfort temperature index, human heat production, gas compression basics, minimum SEER standards, evaporative cooler operation, refrigerant compressor types, condenser water treatment, economizer controls, and cooling load calculation 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.

Thermodynamic fundamentals: Boyle's Law — at constant temperature, pressure and volume are inversely proportional (P₁V₁ = P₂V₂). Latent heat of vaporization is the energy required to change liquid to vapor at constant temperature. ASHRAE recommends indoor relative humidity between 30-60% for comfort. Minimum residential SEER has been 13-14 depending on climate zone; always verify current DOE minimum for the specific region.

25

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45 min

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70%

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HVAC Air Conditioning Practice Test 2 — Question List

Question 1: The heat which changes the state of substance is …………….

Latent heat
Sensible heat
Super heat
Dew heat

Question 2: What is the band of relative humidity (RH) that should be maintained as per ASHRAE standard?

25 and 60%
15 and 30%
60 and 70%
45 and 80%

Question 3: Under constant temperature the absolute pressure of a gas varies …………….. as its volume

Inversely
Proportionally
Double
Same

Question 4: Which of the following is compressed in air conditioning equipment?

Refrigerant gas
Air
Hydrogen gas
Argon gas

Question 5: Which of the following parameters determines the ventilation requirements of a given structure or space?

Number of occupants in the space
Air temperature in the space
Moisture in the space
Size of the space

Question 6: The purpose of cleaning and filtering the air in air conditioning unit is to …………….

Remove the moisture from air
Remove the dust and other contaminants from air
Add the moisture to the air

Question 7: The comfort chart that is published by ASHRAE is an empirically determined effective …………. Index.

Temperature
Pressure
Flow
Humidity

Question 8: What is the general cooling estimation usually given for a person?

200 Btu
150 Btu
250 Btu
100 Btu

Question 9: 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 10: What should be the minimum SEER rating for a new air conditioning unit?

10
8
6
5

Question 11: How does an evaporative cooler (swamp cooler) work, and why is it only effective in dry climates?

Evaporative coolers work best in humid climates because the moisture in the air helps the evaporation process
Evaporative coolers work by evaporating water to cool air and are only effective in dry climates where the air has capacity to absorb moisture; humid air cannot support adequate evaporation
Evaporative coolers cool air using a refrigerant coil with water as the secondary fluid
Evaporative coolers are effective in all climates but use more energy in humid areas

Question 12: What is "volumetric efficiency" in a reciprocating compressor and what reduces it?

Volumetric efficiency refers to the volume of cooling water used per ton of refrigeration
Volumetric efficiency is the ratio of actual vs. theoretical refrigerant mass drawn into the cylinder; it is reduced by clearance volume re-expansion, high compression ratios, leaking valves, and hot suction gas
Volumetric efficiency only matters in large commercial compressors — residential compressors always operate at 100% VE
Higher compression ratios always improve volumetric efficiency

Question 13: Why is Legionella bacteria a concern in cooling towers, and what water treatment measures prevent its growth?

Legionella is only a concern in drinking water systems — cooling towers do not require any special water treatment
Legionella thrives in cooling tower water temperatures; prevention requires biocide treatment, drift eliminators, basin cleaning, and a written Water Management Plan per ASHRAE 188
Cooling towers use only copper pipes which naturally prevent Legionella growth without chemical treatment
Legionella can be eliminated by adding chlorine to cooling towers once per year

Question 14: A building's air-side economizer is stuck in the "fully open" position on a hot, humid summer day. What are the consequences?

A stuck-open economizer on a hot day improves efficiency because it brings in fresh cool outdoor air
A stuck-open economizer on a hot, humid day forces the HVAC to cool large volumes of hot outdoor air, overwhelming the system and causing high indoor temperatures, humidity, and energy consumption
A stuck economizer cannot cause cooling problems because the refrigeration system automatically compensates for changes in outdoor air volume
An economizer stuck open only affects ventilation — it has no effect on indoor temperature or humidity

Question 15: What are the main heat gain sources that must be included in a cooling load calculation for a commercial office building?

Only the outdoor temperature needs to be considered — internal heat gains have no effect on cooling loads
Major cooling load sources include solar heat gain through glass, wall/roof conduction, occupant heat (250 BTU/hr sensible + 200 BTU/hr latent each), lighting (3.412 BTU/W), equipment, and ventilation
The cooling load calculation only includes the size of the space — no other factors matter
Internal heat gains (people, lights, equipment) are not included in cooling loads because they are offset by the heat pump heating cycle

Question 16: What is Charles' Law and how does it apply to HVAC and refrigeration systems?

Charles' Law states that gas pressure and temperature are inversely proportional at constant volume
Charles' Law states that at constant pressure, gas volume is directly proportional to absolute temperature — explaining why hot gas expands and why refrigerant cylinder pressure rises with temperature
Charles' Law is not used in HVAC — it only applies to industrial gas systems
Charles' Law states that equal volumes of all gases contain equal numbers of molecules at the same temperature and pressure

Question 17: How does a technician use a refrigerant pressure-temperature (P-T) chart to determine if a system is operating correctly?

P-T charts are only used during initial charging — they have no diagnostic value during service calls
P-T charts convert measured system pressure to saturation temperature; technicians then calculate superheat (suction line temp − saturation temp) and subcooling (saturation temp − liquid temp) to assess charge and performance
P-T charts determine the maximum allowable pressure for each refrigerant before the cylinder must be replaced
P-T charts only apply to R-22 — modern refrigerants do not follow predictable pressure-temperature relationships

Question 18: What is TAB (Testing, Adjusting, and Balancing) in HVAC and why is it important after a new system installation?

TAB is a fire alarm testing procedure required by NFPA for HVAC systems
TAB (Testing, Adjusting, and Balancing) measures and adjusts air and water flows so each zone receives the design CFM/GPM, ensuring comfort, efficiency, and code compliance after installation
TAB is only required for commercial systems over 20 tons — residential HVAC does not need air balancing
TAB is performed only on the refrigerant circuit — ductwork is not part of the balancing process

Question 19: How does a Variable Air Volume (VAV) air distribution system work and what are its advantages over a constant volume system?

VAV systems vary the supply air temperature to each zone — all zones receive the same airflow at different temperatures
VAV systems use modulating dampers in each zone to vary airflow from minimum to maximum; the supply fan slows at part load saving significant energy because fan power varies with the cube of fan speed
VAV systems are only used in residential applications — commercial systems always use constant volume
VAV boxes open and close to prevent humidity — temperature control is not the primary function

Question 20: Why is 55°F the typical supply air temperature in commercial air conditioning, and what are the trade-offs of using a higher or lower supply air temperature?

55°F supply air was arbitrarily chosen by ASHRAE with no thermodynamic basis
55°F supply air is at or below the dew point of typical room air, allowing dehumidification while cooling; higher supply temp saves chiller energy but may not dehumidify; lower increases moisture removal but uses more energy
The supply air temperature is always 55°F regardless of climate or application — it is a fixed standard
Lower supply temperatures always decrease system energy consumption because the refrigeration system runs less frequently

Question 21: How can a service technician determine what type of refrigerant is in an existing air conditioning system without laboratory analysis?

Guess based on the system's age — all systems installed before 2005 use R-22 and all newer ones use R-410A
Check the equipment nameplate (most reliable), compare system pressures to P-T chart, or use a refrigerant identifier tool — never add refrigerant to an unknown or suspected mixed system
Refrigerant type does not matter — all HFC refrigerants can be mixed and used interchangeably
Refrigerant can only be identified in a laboratory — no field identification method is reliable

Question 22: What is SEER2 and why did the DOE introduce it to replace the previous SEER standard?

SEER2 is simply a marketing term for units with SEER ratings above 20 — it has no different test methodology
SEER2 uses more realistic test conditions (higher external static pressure) than old SEER, resulting in 5-7% lower values for the same equipment; DOE mandated it to better reflect real-world efficiency
SEER2 applies only to heat pumps — air conditioners are still rated using the old SEER standard
SEER2 values are always higher than SEER — manufacturers prefer it because it shows their equipment in a better light

Question 23: How is CO2 concentration used as a demand-controlled ventilation (DCV) signal and what is the target concentration for acceptable indoor air quality?

CO2 above 400 ppm indicates immediate health danger and requires emergency ventilation
CO2 is used as a DCV signal — indoor CO2 should stay below ~1,100 ppm to indicate adequate ventilation; DCV opens dampers as CO2 rises (higher occupancy) and closes them when CO2 drops to save energy
CO2 sensors measure cooling load — higher CO2 means more heat gain and calls for more cooling
Outdoor air dampers should always be fully open regardless of CO2 levels to maximize fresh air

Question 24: Why is the suction line insulated in an air conditioning system but the liquid line typically is not?

Both suction and liquid lines must be insulated — no refrigerant line should be left exposed
The suction line is insulated to prevent excess superheat gain and condensation because it is cold (40-55°F); the liquid line is typically not insulated because it runs at a higher temperature than ambient in most installations
The liquid line is insulated and the suction line is not — the suction line benefits from absorbing heat from the surroundings
Neither line needs insulation — the refrigerant pressure protects the lines from temperature changes

Question 25: What is the AIM Act and how does it affect the HVAC industry?

The AIM Act requires all existing HVAC equipment to be replaced immediately with new lower-GWP systems
The AIM Act phases down HFC production by 85% over 15 years; for HVAC, it drives the transition from R-410A (GWP 2,088) to A2L alternatives like R-454B (GWP 466) and R-32 (GWP 675)
The AIM Act only applies to refrigerants used in automobiles — residential HVAC is not affected
Under the AIM Act, technicians must replace R-410A systems immediately if they are found to have a refrigerant leak

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

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Source: NEC 2026 Art. 440 & electrical theory