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HVAC NEC 2023

HVAC Air Conditioning Practice Test 3

Free HVAC Air Conditioning Practice Test 3. 25 questions on evaporative cooling effects, cold water temperature ranges for cooling, compressor-generated pressure differences, head pressure relationship to horsepower, duct velocity and friction loss, BHP and RPM relationships, tons of refrigeration (1 ton = 12,000 BTU/hr), sensible heat and latent heat removal, sensible heat definition, Boyle's Law pressure-volume relationships, refrigerant contaminants, compressor lubrication, expansion valve operation, condenser sizing, and cooling coil dehumidification.

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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 fact: 1 ton of refrigeration = 12,000 BTU/hr. This is based on the heat of fusion of ice: to melt 1 ton (2,000 lbs) of ice in 24 hours requires 2,000 × 144 BTU/lb ÷ 24 hours = 12,000 BTU/hr. The brake horsepower (BHP) of a centrifugal fan varies with the CUBE of the RPM — doubling fan speed increases power requirement 8 times! This cubic relationship is why variable speed drives save so much energy when fans slow down.

25

Questions

45 min

Time

70%

Pass

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HVAC Air Conditioning Practice Test 3 — Question List

Question 1: An evaporative cooling method cools the indoor air by lowering its wet bulb temperature and by increasing its dry bulb temperature.

True
False

Question 2: What should be temperature range of water used for cold-water coil cooling method?

35<sup>0</sup> F to 55<sup>0</sup>F
40<sup>0</sup> F to 65<sup>0</sup>F
15<sup>0</sup> F to 25<sup>0</sup>F
10<sup>0</sup> F to 45<sup>0</sup>F

Question 3: Which of the following is the primary purpose of the compressor in refrigeration system?

Establishing a pressure difference in the system
Increasing the refrigerant flow in the system
Increasing the temperature of the refrigerant at inlet of condenser
To pump the refrigerant the refrigerant throughout the system

Question 4: If the system head increases, the fan need …………. horse power to pump air through the system.

High
Low

Question 5: What should be air velocity in the air ducts to minimize the effect of frictional losses?

High
Low
Moderate

Question 6: Brake hose power on the fan motor varies as directly ………….. of the fan rpm ratio.

Cube
Square
Quadruple

Question 7: A ton of refrigeration is equal to …………

12,000 Btu per hour
1200 Btu per hour
1500 Btu per hour
1000 Btu per hour

Question 8: In order to meet minimal standards of comfort ………………… must be reduced to an acceptable level

Latent heat of the air
Sensible heat of the air
Both latent and sensible heat of the air

Question 9: The heat which changes the temperature of substance is …………………..

Latent heat
Sensible heat
Super heat
Dew heat

Question 10: Under constant temperature the absolute pressure of a gas varies …………….. as its volume

Inversely
Proportionally
Double
Same

Question 11: What are the three main contaminants that can damage an air conditioning system if introduced with the refrigerant or during service?

The three main contaminants are: UV dye, excess oil charge, and oversized expansion valve
The three main refrigerant system contaminants are moisture (causes acid and ice plugging), air/non-condensables (raises head pressure), and wrong oil type (immiscibility, poor lubrication)
The only harmful contaminant is excessive refrigerant charge — other contaminants are self-correcting
Air is not a contaminant in AC systems because it is inert and does not react with refrigerants

Question 12: How is the compressor in a hermetic refrigeration system lubricated and why is this critical?

Hermetic compressors do not require lubrication — the refrigerant itself acts as the lubricant
Oil circulates with refrigerant through the entire system and must be miscible with the refrigerant; improper oil type or liquid refrigerant dilution causes compressor bearing damage
Oil is added through the suction line annually during preventive maintenance regardless of operating condition
Lubrication is only needed for open-drive compressors — hermetic compressors have no moving parts that require oil

Question 13: How does a Thermostatic Expansion Valve (TXV) modulate refrigerant flow to maintain consistent superheat?

The TXV is powered by a small electric motor that adjusts opening based on a thermostat signal
The TXV uses three competing pressure forces (sensing bulb opens; evaporator pressure and spring close) to automatically maintain constant superheat as system conditions change
The TXV maintains constant refrigerant flow regardless of system load — it is not a modulating device
The TXV senses discharge pressure to adjust flow — higher head pressure opens the valve to protect the compressor

Question 14: What happens to an air conditioning system's efficiency and capacity if the condenser is undersized for the application?

An undersized condenser improves efficiency by keeping refrigerant at higher pressure for better compression
An undersized condenser cannot reject heat fast enough, causing high head pressure, reduced capacity, high compressor discharge temperature, and possible high-pressure safety trip
An undersized condenser causes low head pressure because less refrigerant can condense
Condenser size does not affect system efficiency — only the evaporator coil size determines cooling capacity

Question 15: Why does a cooling coil simultaneously cool and dehumidify the air, and what determines how much moisture is removed?

The cooling coil removes moisture using a chemical desiccant that activates at low temperature
When the coil surface is below the air's dew point, moisture condenses on the fins; the amount removed depends on coil surface temperature, face velocity (contact time), and entering air moisture content
Dehumidification and cooling are separate processes — they do not occur simultaneously on the same coil
All moisture is removed from the air by the air filter before it reaches the coil

Question 16: What is an Energy Recovery Ventilator (ERV), how does it differ from an HRV, and when should each be used?

ERV and HRV are identical — they use the same components and have the same application
ERV transfers both heat and moisture between exhaust and supply air; HRV transfers heat only. ERVs are better in humid climates; HRVs are better in cold-dry climates where removing interior moisture is beneficial
ERVs heat incoming outdoor air in winter and HRVs cool it in summer — they have opposite seasonal functions
ERVs are only used in commercial buildings — residential ventilation always uses HRVs

Question 17: Why does a commercial kitchen hood exhaust system require makeup air, and what problems arise without it?

Commercial kitchen exhaust hoods are self-contained — no makeup air is needed because they recirculate the kitchen air
Kitchen hoods exhaust large volumes (1,000-8,000+ CFM per hood); without makeup air the kitchen becomes severely negatively pressurized causing door problems, hood spillover, flame disturbance, and CO risk
Makeup air for kitchen hoods should always be refrigerated to offset the heat from the cooking equipment
Makeup air is required only when the kitchen exhaust exceeds 10,000 CFM — smaller kitchens do not need it

Question 18: For systems containing 50 or more pounds of refrigerant, what does EPA Section 608 require when the system exceeds its annual leak rate threshold?

No leak repair is required — the EPA only tracks refrigerant purchases, not system leak rates
Systems ≥50 lbs exceeding 30% annual leak rate must have leaks repaired within 30 days or develop a retirement plan; records of refrigerant added must be kept for 3 years
Any refrigerant leak regardless of system size requires immediate emergency shutdown and EPA notification
Leak rates only matter for R-22 systems — HFC systems can leak any amount without regulatory action

Question 19: Scroll compressors have built-in protection against reverse rotation. Why is reverse rotation dangerous and what can cause it?

Scroll compressors can rotate in either direction — they are designed to operate bidirectionally
Reverse rotation causes no compression and thrust bearing damage; caused by wrong three-phase wiring sequence or back-spin; detected by characteristic noise and confirmed by checking phase sequence
Reverse rotation in a scroll compressor improves efficiency at low load by reducing compression work
Reverse rotation is only possible in reciprocating compressors — scroll compressors cannot reverse rotate

Question 20: Why does condensation form inside wall cavities in air-conditioned buildings in hot-humid climates, and how can it be prevented?

Condensation in walls only occurs in cold climates — hot climates never have this problem
In hot-humid climates, outdoor moisture diffuses through walls into cooler, drier interiors; if wall temperature drops below the outdoor dew point, condensation forms — prevented by continuous exterior insulation and vapor retarder on the exterior side
An interior vapor barrier (plastic sheet) on the inside of walls prevents condensation in all climates
Wall condensation is harmless and does not cause structural damage

Question 21: What is the relationship between COP and EER for a cooling system, and how is EER converted to COP?

EER and COP are identical metrics with no conversion needed between them
EER = BTU/hr ÷ Watts; COP = EER ÷ 3.412 (converting BTU/hr to Watts). A system with EER 10 has COP = 2.93
COP = EER × 3.412 because you multiply by the conversion factor from Watts to BTU/hr
COP applies only to heating systems — cooling systems use only EER as the efficiency metric

Question 22: What is the difference between a supply diffuser and a return grille, and what design principle guides their placement?

Supply diffusers and return grilles are interchangeable — they can be installed in any location
Supply diffusers spread conditioned air into the room from the supply duct; return grilles draw room air back. Supply diffusers should wash exterior walls in cooling applications to intercept heat gain at its source
Return grilles should always be placed directly across from supply diffusers for maximum airflow
Supply diffusers should be placed in interior locations to keep conditioned air away from hot exterior walls

Question 23: What is the recommended maximum air velocity in residential supply ducts, and what happens when duct velocity is too high?

Higher duct velocity is always better because it delivers more air with less duct material
Residential supply ducts should be limited to 700-900 FPM; excessive velocity causes noise, high friction loss (∝ velocity²), and increased duct leakage
There is no maximum duct velocity — the system can operate at any speed as long as the fan can handle it
Duct velocity does not affect noise — only the diffuser face velocity causes sound issues

Question 24: Why do commercial buildings require multiple HVAC zones or systems rather than a single central unit?

Commercial buildings use multiple systems only to provide redundancy — a single system would work equally well
Different building areas have vastly different and simultaneous heating/cooling requirements (perimeter vs. interior, solar exposure, occupancy variation) that a single system cannot satisfy
Code requires one separate HVAC unit per floor in any building over 3 stories
Multiple zones are only needed in buildings over 100,000 sq ft — smaller commercial buildings use a single system

Question 25: What is building commissioning (Cx) and how does it differ from simple HVAC startup and TAB?

Building commissioning is the same as the city building inspection — the inspector checks if systems are installed correctly
Building commissioning (Cx) is a formal quality process verifying all systems meet the owner's requirements through design review, installation inspection, functional performance testing, and staff training
Commissioning only covers HVAC systems — electrical, plumbing, and fire protection are inspected separately by other parties
Commissioning is an optional service only needed for LEED-certified buildings

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