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HVAC NEC 2023

HVAC Air Conditioning Practice Test 1

Free HVAC Air Conditioning Practice Test 1. 25 questions on humidification, dew point, latent heat, return air ductwork, atmospheric pressure, altitude effects on pressure, absolute pressure, vaporization pressure, psychrometric readings, ASHRAE ventilation standards, sensible heat ratio, cooling coil selection, air-side economizer operation, cooling tower basics, and refrigerant circuit component identification.

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Frequently Asked Questions

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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 psychrometric concepts: Dew point is the temperature at which air must be cooled (at constant pressure) before water vapor begins to condense. Latent heat is heat that causes a change of state (e.g., water → water vapor) without changing temperature. Sensible heat changes temperature without changing state. Standard atmospheric pressure at sea level is 14.696 psi (not an NEC code reference). ASHRAE 62.1 sets ventilation standards: approximately 15-20 CFM of outdoor air per person.

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45 min

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HVAC Air Conditioning Practice Test 1 — Question List

Question 1: Which of the following is called as humidification?

Adding moisture to air
Removing moisture from air
Adding heat to the air
Removing heat from the air

Question 2: 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 3: The amount of heat contained in the water vapor of air is called as ………….

Latent heat
Sensible heat
Dew heat
Heat capacity

Question 4: What is the function of return duct in air conditioning system?

Returns the air from the air-conditioned rooms back to central supply rooms.
It aids the supply fan to provide the air for corners of the building
It is used to exhaust air from the building
Provides outside air to the building

Question 5: What is the air pressure at standard atmosphere?

14.7 inches of mercury
14.7 psi
29.9 pounds per square inch
29.7 psia

Question 6: How much of atmospheric pressure will decrease with increase in altitude of 1000 feet?

½ lb
1 lb
1 ½ lb
2 lb

Question 7: When a steam gauge measures the pressure in the boiler is 6 lbs, what is its equivalent absolute pressure in the boiler?

20.7 lbs
35.9 lbs
6 lbs
8.7 lbs

Question 8: The vaporization pressure of liquid ……………. As the pressure on the liquid increases?

Increases
Decreases
Remains unchanged

Question 9: Which of the following meter is used to measure relative humidity?

Psychrometer
Thermometer
Barometer

Question 10: According to ASHRAE, which of the following are the outside fresh air requirements?

10 cfm to 20 cfm
20 cfm to 40 cfm
5 cfm to 10 cfm
8cfm to 10 cfm

Question 11: What is the Sensible Heat Ratio (SHR) of a cooling coil and how does it affect coil selection for different applications?

SHR is the ratio of supply air temperature to return air temperature and determines coil size
SHR = sensible load ÷ total load; it determines how much temperature reduction vs. moisture removal the coil provides — lower SHR removes more moisture, needed in humid climates
SHR stands for System Heat Rating and is the maximum BTU/hr capacity of the cooling system
SHR only applies to commercial systems — residential cooling coils are not rated for SHR

Question 12: How does an air-side economizer work and under what conditions should it be activated?

An air-side economizer recirculates exhaust air through an additional cooling coil to pre-cool it before it enters the supply
An air-side economizer opens outdoor air dampers to provide free cooling when outdoor temperature/enthalpy is lower than the return air, reducing or eliminating mechanical refrigeration
An air-side economizer is a water-cooled pre-cooler mounted on the outdoor unit to reduce head pressure
Air-side economizers are only used in heating mode — they have no cooling function

Question 13: What is a cooling tower and how does it reject heat from a water-cooled chiller system?

A cooling tower rejects heat using dry outdoor air only — no water evaporation is involved
A cooling tower rejects heat primarily through evaporative cooling — water evaporation carries away latent heat, cooling condenser water to near the outdoor wet-bulb temperature
A cooling tower is used for heating purposes in winter, acting as a supplemental heat source for the chiller
Cooling towers are only used in residential heat pump systems in desert climates

Question 14: What is the function of the filter-drier in an air conditioning system and where is it located?

The filter-drier is located in the suction line to remove moisture from refrigerant before it reaches the compressor
The filter-drier is in the liquid line between condenser and metering device; it filters particles and adsorbs moisture to prevent metering device plugging and acid formation
The filter-drier is only needed in systems with R-22 — modern R-410A systems do not require driers
The filter-drier is located after the metering device to protect the evaporator coil from contamination

Question 15: A service technician observes bubbles in the liquid line sight glass during system operation. What does this indicate?

Bubbles in the liquid line sight glass indicate the system is operating normally — some vapor is always present
Bubbles in the sight glass indicate flash gas — caused by undercharge, liquid line restriction, or insufficient subcooling — refrigerant is vaporizing before reaching the metering device
Bubbles indicate the liquid line is freezing and the system should be shut down immediately
Bubbles only appear in the sight glass when the outdoor temperature exceeds 100°F

Question 16: What is the difference between an air-cooled chiller and a water-cooled chiller, and which is more efficient?

Air-cooled chillers are always more efficient because they don't require the energy to pump condenser water
Water-cooled chillers are 20-30% more efficient because they reject heat to the cooler wet-bulb temperature via a cooling tower, but require more infrastructure than air-cooled units
Both types have identical efficiency — the choice is based only on space availability
Water-cooled chillers are only used in cold climates where outdoor air is too cold for air cooling

Question 17: What causes an air conditioning evaporator coil to ice up during operation, and how should a technician diagnose which cause is responsible?

Evaporator icing always indicates refrigerant overcharge — remove refrigerant to fix it
Evaporator icing is caused by low airflow, low refrigerant charge, low outdoor temperature, or metering device problems — diagnose by checking airflow first, then refrigerant charge
Icing is normal during summer operation and does not indicate a problem
Icing only occurs in commercial systems — residential AC units are designed to prevent coil freezing

Question 18: A sight glass moisture indicator has turned from green to yellow. What action must a technician take?

A yellow sight glass is normal during the first hour of operation and will return to green on its own
Yellow indicator means moisture is present; replace the filter-drier, recover refrigerant, evacuate thoroughly to 500 microns, and test for acid if the system has been wet for some time
A yellow sight glass only means the refrigerant charge is low — add refrigerant until the indicator turns green
The sight glass moisture indicator color change is a calibration drift — the indicator does not need replacement or action

Question 19: What is a VRF (Variable Refrigerant Flow) system and how does it differ from a multi-split mini-split system?

VRF systems are identical to multi-split systems but use larger refrigerant lines
VRF systems use variable-speed compressors and electronic expansion valves to serve many zones (8-64+); VRF-HR types can simultaneously heat and cool different zones by transferring heat between them
VRF stands for Variable Refrigerant Fluid — it uses water as a refrigerant instead of chemical refrigerants
VRF is only used in residential applications because the refrigerant piping cannot be installed in commercial buildings

Question 20: What are the main types of humidifiers used in commercial HVAC systems and how does each add moisture to the air?

All humidifier types work the same way — only the water source differs between models
Main types include electric steam (most hygienic, highest cost), evaporative media (simple, lower cost, bacteria risk), and ultrasonic (low energy, requires distilled water) — each adds moisture differently
Humidifiers are not used in commercial HVAC because code prohibits adding moisture to supply air
All commercial buildings use only spray-type humidifiers because they are the most cost-effective option

Question 21: What does "external static pressure" mean in an air handling unit specification, and how does it affect fan and motor selection?

External static pressure is the pressure of refrigerant at the expansion valve before it enters the evaporator
External static pressure is the total airside resistance (duct friction, filters, coils, fittings) that the fan must overcome; higher ESP means less airflow at the same fan speed
External static pressure only affects the supply side — the return side has no resistance for the fan to overcome
External static pressure is fixed by the manufacturer and cannot be changed by ductwork design

Question 22: Why is building pressurization important in HVAC design and what problems occur when a building is negatively pressurized?

Negative building pressurization is preferred because it helps the HVAC system exhaust heat more efficiently
Negative pressurization causes uncontrolled infiltration of humid, dirty outdoor air, door drafts, odors entering from outside, mold risk, and possible combustion appliance backdraft
Building pressurization has no effect on indoor air quality — only filtration matters
Positive pressurization must never exceed 0 Pascals because it will over-pressurize the building and pop windows

Question 23: What is IPLV and why is it a better efficiency metric than full-load efficiency (kW/ton) for evaluating chillers?

IPLV and full-load kW/ton are identical metrics — they measure the same efficiency point
IPLV is a weighted efficiency metric at 25-100% load; it better represents annual energy cost than full-load efficiency because chillers spend most operating hours at part load
IPLV only applies to residential air conditioners — commercial chillers are rated only by full-load kW/ton
Higher IPLV values indicate better efficiency — the higher the IPLV number, the lower the operating cost

Question 24: According to ASHRAE 62.1, what are the two components of the outdoor air ventilation rate requirement for an occupied space?

ASHRAE 62.1 requires only a fixed minimum CFM per person regardless of room size
ASHRAE 62.1 requires both a people-related component (CFM/person for bioeffluents) and an area-related component (CFM/sq ft for material off-gassing)
ASHRAE 62.1 ventilation requirements are based only on total building square footage, not occupancy
ASHRAE 62.1 is not applicable to HVAC — it only covers industrial ventilation for chemical hazards

Question 25: What is the difference between a direct expansion (DX) cooling system and a chilled water (CHW) cooling system?

DX and chilled water systems are identical — only the pipe material differs
DX systems circulate refrigerant directly to the coil at the air handler; chilled water systems use a central chiller to produce cold water pumped to remote AHUs — preferred for large, multi-zone buildings
Chilled water systems are only used in residential buildings because they cannot cool large volumes of air
DX systems are more efficient than chilled water systems because they eliminate the intermediate water loop energy loss

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