Are flashcards effective for the NATE exam?

Yes. Flashcards use active recall — retrieving an answer from memory — which research shows is one of the most effective study methods, especially in short, spaced sessions. They're ideal for the exam's load of formulas, definitions, and component facts.

What topics do the NATE flashcards cover?

All seven KATE areas: Basic Electricity, Safety, Achieving Desired Conditions, Taking Temperature and Humidity Measurements, Tools, Using Basic Science (the refrigeration cycle and heat transfer), and Basic Construction.

How should I study with these NATE flashcards?

Lead with the highest-yield areas — Basic Electricity and Safety, which carry the most questions — then drill the rest. Mix the modes: flip to learn, type to test recall, match for speed, and quiz to check yourself before a full practice test.

Are the NATE flashcards free?

Yes — 100% free, all four study modes, no paywall.

Do these flashcards match the current NATE exam?

Yes. The cards are organized to the current NATE Core KATE knowledge areas, covering all seven areas the Core exam tests, and they reinforce the fundamentals that carry into the specialty exams.

Refrigeration cycle: the 4 components in order?

Compressor → condenser → metering device → evaporator → back to the compressor.

Where does cooling actually happen in an AC?

The evaporator — low-pressure refrigerant boils and absorbs heat from the indoor air.

Where is heat rejected in an AC system?

The condenser (high side) — hot vapor releases heat to the outdoor air and condenses to liquid.

Job of the compressor?

It is the pump — it raises the pressure and temperature of low-pressure vapor and circulates refrigerant.

Job of the metering device (TXV/orifice)?

Drops pressure and meters refrigerant flow into the evaporator; splits the high and low sides.

Does an air conditioner create cold?

No — it moves heat. Heat is absorbed at the evaporator and rejected at the condenser.

What divides the high side from the low side?

The compressor and the metering device.

Sensible heat vs latent heat?

Sensible heat changes temperature; latent heat changes state (phase) with no temperature change.

Degrees a refrigerant vapor is above its saturation (boiling) temperature once it is 100% vapor.

Degrees a refrigerant liquid is below its saturation (condensing) temperature.

How is subcooling calculated?

Condensing saturation temperature − measured liquid-line temperature (e.g., 105° − 95° = 10°).

Why does superheat matter?

It confirms only vapor (never damaging liquid) returns to the compressor.

Three modes of heat transfer?

Conduction (contact), convection (fluid motion), radiation (electromagnetic waves).

British Thermal Unit — heat to raise 1 lb of water by 1°F.

What is saturation temperature?

The temperature at which a refrigerant changes state at a given pressure; liquid and vapor coexist.

The total heat content of a substance (sensible + latent), in BTU per pound.

Why does refrigerant boil colder at low pressure?

A refrigerant's saturation (boiling) temperature drops as its pressure drops.

Conduction example in HVAC?

A warm copper line heating a fitting it touches.

Convection example in HVAC?

Warm air rising off a furnace; a blower moving conditioned air.

Radiation example in HVAC?

The sun warming a roof; an infrared heater warming objects.

At constant temperature, halving a gas's pressure doubles its volume (P and V are inversely related).

Why use absolute temperature in gas-law math?

The gas laws are based on absolute zero; using °F/°C directly gives wrong results.

Dalton's law of partial pressures?

Total pressure of a gas mixture equals the sum of each gas's partial pressure.

A solid changing directly to a gas without becoming liquid (e.g., dry ice).

V = I × R (voltage = current × resistance).

Electrical power formula?

P = V × I (watts = volts × amps).

Current of a 1500 W heater on 120 V?

I = P ÷ V = 1500 ÷ 120 = 12.5 amps.

Power of a 60 Ω resistor on 120 V?

P = V² ÷ R = 120² ÷ 60 = 14,400 ÷ 60 = 240 watts.

Series circuit: current?

The same at every point in the circuit.

Series circuit: resistance?

Resistances add (R total = R1 + R2 + …).

Series circuit: voltage?

Voltage divides across the loads (three equal loads on 120 V drop 40 V each).

Parallel circuit: current?

Current divides among the branches.

Parallel circuit: total resistance?

Less than the smallest individual branch resistance.

Unit of voltage / current / resistance / power?

Volts / amperes / ohms / watts.

Your FREE NATE Flashcards 2026 – 250+ Cards

Realistic, NATE exam-style HVAC flashcards across all 7 KATE areas — flip, match, type, and quiz yourself.

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NATE Flashcards

Refrigeration cycle: the 4 components in order?: Compressor → condenser → metering device → evaporator → back to the compressor.
Where does cooling actually happen in an AC?: The evaporator — low-pressure refrigerant boils and absorbs heat from the indoor air.
Where is heat rejected in an AC system?: The condenser (high side) — hot vapor releases heat to the outdoor air and condenses to liquid.
Job of the compressor?: It is the pump — it raises the pressure and temperature of low-pressure vapor and circulates refrigerant.
Job of the metering device (TXV/orifice)?: Drops pressure and meters refrigerant flow into the evaporator; splits the high and low sides.
Does an air conditioner create cold?: No — it moves heat. Heat is absorbed at the evaporator and rejected at the condenser.
What divides the high side from the low side?: The compressor and the metering device.
Sensible heat vs latent heat?: Sensible heat changes temperature; latent heat changes state (phase) with no temperature change.
What is superheat?: Degrees a refrigerant vapor is above its saturation (boiling) temperature once it is 100% vapor.
What is subcooling?: Degrees a refrigerant liquid is below its saturation (condensing) temperature.
How is subcooling calculated?: Condensing saturation temperature − measured liquid-line temperature (e.g., 105° − 95° = 10°).
Why does superheat matter?: It confirms only vapor (never damaging liquid) returns to the compressor.
Three modes of heat transfer?: Conduction (contact), convection (fluid motion), radiation (electromagnetic waves).
Heat always flows in which direction?: From warmer to cooler.
1 ton of cooling = how many BTU/hr?: 12,000 BTU/hr.
Specific heat of water?: 1 BTU per pound per °F.
Latent heat of vaporization of water?: ≈ 970 BTU/lb (at 212°F).
Latent heat of fusion of water?: ≈ 144 BTU/lb (at 32°F).
What is a BTU?: British Thermal Unit — heat to raise 1 lb of water by 1°F.
What is saturation temperature?: The temperature at which a refrigerant changes state at a given pressure; liquid and vapor coexist.
What is enthalpy?: The total heat content of a substance (sensible + latent), in BTU per pound.
Why does refrigerant boil colder at low pressure?: A refrigerant's saturation (boiling) temperature drops as its pressure drops.
Conduction example in HVAC?: A warm copper line heating a fitting it touches.
Convection example in HVAC?: Warm air rising off a furnace; a blower moving conditioned air.
Radiation example in HVAC?: The sun warming a roof; an infrared heater warming objects.
Boyle's law (gas)?: At constant temperature, halving a gas's pressure doubles its volume (P and V are inversely related).
Why use absolute temperature in gas-law math?: The gas laws are based on absolute zero; using °F/°C directly gives wrong results.
Dalton's law of partial pressures?: Total pressure of a gas mixture equals the sum of each gas's partial pressure.
Sublimation?: A solid changing directly to a gas without becoming liquid (e.g., dry ice).
Order of state change gaining energy?: Solid → liquid → gas.
Ohm's law?: V = I × R (voltage = current × resistance).
Find current from Ohm's law?: I = V ÷ R.
Find resistance from Ohm's law?: R = V ÷ I.
Electrical power formula?: P = V × I (watts = volts × amps).
Power when current is unknown?: P = V² ÷ R.
Power form using current and resistance?: P = I² × R.
Current of a 1500 W heater on 120 V?: I = P ÷ V = 1500 ÷ 120 = 12.5 amps.
Power of a 60 Ω resistor on 120 V?: P = V² ÷ R = 120² ÷ 60 = 14,400 ÷ 60 = 240 watts.
Series circuit: current?: The same at every point in the circuit.
Series circuit: resistance?: Resistances add (R total = R1 + R2 + …).
Series circuit: voltage?: Voltage divides across the loads (three equal loads on 120 V drop 40 V each).
Parallel circuit: voltage?: The same across each branch.
Parallel circuit: current?: Current divides among the branches.
Parallel circuit: total resistance?: Less than the smallest individual branch resistance.
Unit of voltage / current / resistance / power?: Volts / amperes / ohms / watts.
What is frequency (hertz)?: The number of complete AC cycles per second; U.S. line frequency is 60 Hz.
AC vs DC?: AC reverses direction periodically (line power); DC flows one direction (batteries, ECM internals).
Single-phase vs three-phase power?: Single-phase = one waveform (residential 120/240 V); three-phase = three offset waveforms (commercial, smoother).
Why use three-phase for large motors?: Three offset waveforms give smoother, more efficient motor operation.
Run capacitor vs start capacitor?: Run cap stays in the circuit (efficiency/torque); start cap gives a brief starting boost then drops out.
Capacitor unit of measure?: Microfarads (µF or MFD).
Safety rule for capacitors?: They can hold a dangerous charge after power is off — discharge them safely before handling.
Contactor vs relay?: Contactor switches large continuous loads (compressor/fan); relay switches smaller control loads.
What does a transformer do?: Steps voltage up or down; HVAC controls commonly run on 24 V from a step-down transformer.
Fewer turns on the transformer secondary means?: The secondary voltage is stepped down lower than the primary.
Transformer rated 40 VA — what is VA?: Volt-amperes — its maximum power-handling capacity.
PSC motor?: Permanent split-capacitor — a single-phase induction motor that uses a run capacitor.
ECM motor?: Electronically commutated — a brushless DC motor, variable-speed and high-efficiency, holds constant airflow.
PSC vs ECM efficiency?: ECM is far more efficient and variable-speed; PSC is fixed-speed and lower efficiency.
Purpose of a fuse or circuit breaker?: To open the circuit when current exceeds a safe level, protecting the wiring.
A blown fuse on a normal-draw circuit indicates?: A short circuit or a grounded fault.
What causes a short circuit?: A hot conductor contacting a grounded surface or neutral — a low-resistance path that lets current rise sharply.
What does an ohmmeter measure?: Resistance — and must be used on a de-energized circuit.
Why check motor windings with a megohmmeter?: To verify the very high resistance of winding insulation to ground (insulation quality).
Most accurate analog ohmmeter reading?: Near mid-scale.
What does a multimeter measure?: Voltage, resistance (ohms), and current (amps).
How does a clamp (amp) meter work?: It reads motor current without breaking the circuit, by sensing the magnetic field around a conductor.
Standard U.S. nominal voltages?: 120 / 208 / 240 / 480 V (also 277 V).
What is GFCI protection?: Ground-fault protection for people; it trips at about 4–6 mA of imbalance, far below a breaker's rating.
24 V in HVAC is used for?: Low-voltage control circuits (thermostat, contactor coil, control board).
A bulged or leaking capacitor means?: It has failed and must be replaced.
Common cause of a humming motor that won't start?: A weak or failed run/start capacitor.
Pitted/welded contactor contacts cause?: Poor connection or a stuck-closed circuit on outdoor condensing units.
Wiring diagram vs pictorial diagram?: A wiring/schematic shows the circuit logic; a pictorial shows the physical layout of components.
Lockout/tagout (LOTO) purpose?: To isolate energy, lock/tag it so it can't be re-energized, and verify de-energization before service.
The step techs skip in LOTO?: Verifying the absence of voltage with a meter before touching the equipment.
What OSHA standard covers LOTO?: 29 CFR 1910.147 (control of hazardous energy).
Forms of hazardous energy in HVAC?: Electrical, stored refrigerant pressure, capacitor charge, rotating parts, thermal.
Fire extinguisher Class A?: Ordinary combustibles — wood, paper, cloth, trash.
Fire extinguisher Class B?: Flammable liquids and gases — solvents, oils, gasoline, propane.
Fire extinguisher Class C?: Energized electrical equipment — uses a nonconductive agent.
Fire extinguisher Class D?: Combustible metals — magnesium, sodium, titanium.
Fire extinguisher Class K?: Cooking oils and fats (commercial kitchens).
Which extinguisher for a live electrical fire?: Class C — the only safe choice on energized equipment (an ABC unit qualifies).
What does an ABC dry-chemical extinguisher cover?: Classes A, B, and C — the typical service-van choice.
Why never use water on a live electrical fire?: Water conducts electricity — a shock hazard. De-energize first or use Class C.
PPE that protects eyes from refrigerant?: Safety glasses or goggles (liquid refrigerant can cause frostbite/eye injury).
PPE near loud equipment (chillers/compressors)?: Hearing protection — earplugs or earmuffs.
Ladder 4-to-1 rule?: Place the base 1 foot out for every 4 feet of ladder height.
16-ft ladder at 4-to-1 — base distance?: About 4 feet out from the wall.
Extension ladder height above a roof edge?: At least 3 feet above the edge for safe access.
EPA Section 608 certification — what is it?: Federal certification required to handle refrigerants.
EPA 608 Type I?: Small appliances.
EPA 608 Type II?: High-pressure systems (split systems, heat pumps).
EPA 608 Type III?: Low-pressure systems (chillers).
EPA 608 Universal?: Covers Type I, II, and III.
Is venting refrigerant legal?: No — it is illegal to knowingly vent refrigerant; it must be recovered.
Why pressure-test with nitrogen, not oxygen?: Oxygen combined with refrigerant oil can ignite explosively; use dry nitrogen.
Treat every electrical conductor as?: Energized, until a meter proves otherwise.
What is arc flash?: A dangerous release of energy from an electrical fault; covered by NFPA 70E electrical-safety practices.
Carbon monoxide danger?: Colorless, odorless gas from incomplete combustion; binds to hemoglobin and starves the body of oxygen.
PPE for dust/fibers (suspect asbestos)?: Respiratory protection.
Manifold gauge colors?: Red = high side, blue = low-side compound, yellow = center charging/recovery hose.
What can a compound (blue) gauge read?: Both pressure above atmospheric and vacuum below it.
Why are manifold inner scales refrigerant-specific?: Each refrigerant has a different pressure-temperature relationship.
What is a micron gauge for?: Confirming a deep vacuum (target ≤500 microns) that a compound gauge can't resolve.
Why is a compound gauge inadequate for deep vacuum?: It pegs near 29–30 in. Hg and can't resolve the small changes near a deep vacuum.
Why evacuate a system before charging?: To boil off moisture and remove air and non-condensable gases that harm performance.
Deep-vacuum target with a micron gauge?: 500 microns or below.
What does a vacuum pump do?: Evacuates a system to a deep vacuum to remove air and moisture before charging.
Recovery vs recycle vs reclaim?: Recover = remove refrigerant; recycle = clean on-site; reclaim = restore to virgin spec at a facility.
Why leave vapor space in a recovery cylinder?: So liquid can expand safely without dangerously high pressure as temperature rises (never overfill).
What does a manometer measure?: Gas pressure and air static pressure, in inches of water column.
What does a sling psychrometer measure?: Dry-bulb and wet-bulb temperature, to determine humidity.
What is swaging?: Expanding one tube end so a matching tube slips inside for a brazed joint — no coupling needed.
Why use a tubing bender?: It produces a smooth-radius bend with no added joints to leak or restrict flow.
Purpose of flux when brazing?: It cleans the joint and prevents oxidation so the filler metal flows and bonds.
Electronic (heated-diode) leak detector — how it alarms?: When refrigerant vapor reaches its sensor.
How does UV-dye leak detection work?: Dye circulates and glows at the leak under a UV lamp.
Soap-bubble leak test uses what gas?: Dry nitrogen under pressure — bubbles form at the leak.
Ultrasonic leak detector — what it senses?: The sound of gas escaping under pressure (good in large/noisy systems).
Clamp meter use in HVAC?: Reading a motor's amp draw without breaking the circuit.
Magnehelic-style gauge measures?: Differential (static) pressure across a duct or filter, showing airflow resistance.
Decay (rise) test after evacuation?: Watch for a pressure rise to confirm the system is dry and leak-free.
Dry-bulb temperature?: Ordinary air temperature read by a standard thermometer.
Wet-bulb temperature?: Temperature from a wetted-wick thermometer; evaporation cools it, so it's lower than dry-bulb.
Dew point?: The temperature at which air saturates and water vapor begins to condense.
Order of dry-bulb, wet-bulb, dew point?: Dry-bulb ≥ wet-bulb ≥ dew point for the same air.
At 100% relative humidity, the three temps are?: Equal — dry-bulb = wet-bulb = dew point.
What is relative humidity?: Water vapor in the air vs the most it could hold at that temperature, as a percent.
Why does the wet-bulb show the lowest evaporative temp?: Evaporation removes heat until the air can no longer absorb more moisture.
What is a hygrometer?: An instrument whose only job is to measure the moisture (humidity) of air.
What is a psychrometric chart?: A chart relating dry-bulb, wet-bulb, dew point, RH, humidity ratio, and enthalpy; any two fix the state.
How a thermistor probe senses temperature?: Its electrical resistance changes predictably as its temperature changes.
Calibrate a thermometer in ice water — correct reading?: 32°F.
Ice-water test reads 36°F — what does it mean?: The thermometer is reading 4° high and should be corrected.
Why insert a stem thermometer deeply?: So the sensing portion fully reaches the temperature being measured.
IR thermometer on shiny copper reads low — why?: Low surface emissivity reflects surrounding radiation instead of emitting its own.
Why does a stationary psychrometer need airflow?: Moving air carries away evaporated moisture so evaporation can cool the wet bulb.
Temperature split across a cooling coil?: The dry-bulb drop from return to supply air — a quick operational check.
Probe reading biased toward room air — cause?: Picking up unconditioned surrounding air instead of the duct air.
Wet-bulb depression?: The difference between dry-bulb and wet-bulb temperature; larger = drier air.
7,000 grains equal?: 1 pound of water (humidity ratio is measured in grains per pound of dry air).
Two psychrometric properties fix the air state?: Yes — any two known properties locate a single point on the chart.
Comfort temperature range (rule of thumb)?: ≈ 68–75°F.
Comfort relative-humidity range (rule of thumb)?: ≈ 30–50% (best-practice guidance, not a fixed ASHRAE clause).
Nominal airflow per ton of cooling?: ≈ 400 CFM per ton (band 350–450).
Airflow for a 3-ton system?: ≈ 1,200 CFM (3 × 400).
Lower airflow (~350 CFM/ton) favors?: More dehumidification (latent removal) — good in humid climates.
Higher airflow (~450 CFM/ton) favors?: More sensible cooling — good in dry climates.
Sensible heat airflow formula?: Qs = 1.08 × CFM × ΔT (°F).
Total heat airflow formula?: Qt = 4.5 × CFM × Δh (enthalpy, BTU/lb).
Latent heat airflow formula?: Ql = 0.68 × CFM × ΔW (humidity ratio, grains/lb).
Relationship of total, sensible, latent heat?: Total = sensible + latent (Qt = Qs + Ql).
Why does too little airflow freeze the coil?: Not enough warm air over the coil lets the refrigerant temperature drop below freezing.
Why does short cycling leave the home humid?: Brief runs don't keep the evaporator running long enough to remove much moisture.
What is total external static pressure (TESP)?: Supply + return static pressure; a typical residential target is ≈ 0.5 in. w.c.
Why does warmer air feel less humid at the same moisture?: Warmer air can hold more moisture, so relative humidity is lower.
Why does a cold register sweat in summer?: Its surface dropped to or below the air's dew point, so moisture condenses.
Role of a humidistat?: Senses indoor humidity and switches a humidifier on/off to hold a set level.
Bypass humidifier — what drives airflow through it?: The pressure difference between the higher-pressure supply and lower-pressure return.
When use a fan-powered humidifier?: When there's no convenient return-side connection (its own fan moves the air).
Water panel (evaporative pad) job?: Provides a wetted surface so warm air picks up moisture by evaporation.
Which way does a filter's airflow arrow point?: In the direction of airflow — toward the blower.
Effect of a dirty air filter?: Restricts airflow → lower capacity and possible coil freeze.
Higher MERV filter trade-off?: Captures finer particles but adds airflow resistance — don't over-restrict the blower.
Why keep the air filter clean?: It preserves the design airflow the system was sized for.
High indoor humidity risks?: Mold, mildew, condensation, and material damage.
Very low indoor humidity problems?: Dry air, static electricity, and cracking/shrinking wood.
First thing to check for an airflow problem?: The air filter — a neglected filter is the most common cause.
What is complete combustion of natural gas?: CH₄ + 2 O₂ → CO₂ + 2 H₂O + heat (a clean blue flame).
What does incomplete combustion produce?: Carbon monoxide (CO), soot, and unburned fuel — a yellow, lazy flame.
What does flue-gas analysis measure?: O₂ (excess air), CO₂ (completeness), CO (safety), and stack temperature (efficiency).
What is AFUE?: Annual Fuel Utilization Efficiency — the % of a furnace's fuel energy that becomes usable heat over a year.
AFUE of a standard non-condensing furnace?: ≈ 80% (today's DOE minimum).
AFUE of a high-efficiency condensing furnace?: ≈ 90–98.5% by reclaiming latent heat from flue gases.
Why does a condensing furnace need a drain?: Flue-gas water vapor condenses, producing condensate that must drain away.
Heating value of natural gas?: ≈ 1,000 BTU per cubic foot.
Approximate air-to-gas ratio for combustion?: ≈ 10:1 by volume (with some excess air in practice).
What is stoichiometric combustion?: Burning with exactly the theoretical amount of air for complete combustion.
Why is CO so dangerous physiologically?: It binds to hemoglobin far more readily than oxygen, starving the body of oxygen.
A cracked heat exchanger risk?: Can leak combustion products (including CO) into the conditioned air stream.
What are studs?: The vertical wall framing members in wood-frame construction.
What are joists?: The horizontal framing members that support floors and ceilings.
What are rafters?: The sloped framing members that form the roof.
How should you route a line through a wall?: Through the open bay between studs, away from key structural members.
Where is a load-bearing wall often located?: Running down the center of the house, parallel to the ridge.
What is the floor plan?: The overhead drawing used to locate equipment and runs.
What is a 'clear span'?: The unobstructed distance a structural member crosses without support.
What is a runout?: The branch duct run that feeds a register off the main trunk.
Why insulate and seal ducts in an attic?: Otherwise conditioned air leaks out and unwanted heat transfers in, wasting energy.
How to handle intact suspect asbestos?: Leave it undisturbed and have it assessed — disturbing it releases fibers.
Handling suspect asbestos to be removed?: Stop; do not dry-grind or saw it; follow abatement requirements.
What is a header (in framing)?: A horizontal member spanning an opening (door/window) to carry loads above.
What does R-value measure?: A material's resistance to heat flow — higher R = better insulation.
Relationship of R-value and U-value?: U = 1 ÷ R; a lower U-value (higher R-value) insulates better.
Why does a smooth plastic-tarp-covered roof matter to a tech?: It offers little traction, making slips and falls likely — a fall hazard.
Do insulation R-values add when layered?: Yes — combined R-value is the sum of the layers.
What does a thermostat do?: Senses indoor temperature and signals the system (often via 24 V) to heat or cool.
What is a sequencer in electric heat?: A device that energizes heating elements in stages to limit inrush current.
What is locked-rotor amperage (LRA)?: The high current a motor draws at the instant of starting, before it turns.
What is full-load amperage (FLA / RLA)?: The current a motor draws at its rated running load.
Why does a motor draw high amps if it won't start?: It is near locked-rotor current; a failed capacitor or seized bearing can cause it.
Common-Run-Start (C, R, S) terminals are on?: A single-phase compressor or motor.
What is a potential (start) relay?: A relay that drops the start capacitor out of the circuit once the motor is up to speed.
What is a hard-start kit?: A start capacitor and relay added to boost a struggling compressor's starting torque.
Why discharge a capacitor before testing it?: It can hold a lethal charge even with power off.
Confined-space hazard in a mechanical room?: Refrigerant can displace oxygen; ensure ventilation and monitor before entry.
PPE when brazing?: Eye protection (shaded if needed), gloves, and ventilation for fumes.
Why purge with nitrogen while brazing?: To prevent oxidation (scale) inside the tubing that can foul the system.
Refrigerant on skin can cause?: Frostbite — wear gloves and eye protection.
Step before working on rooftop equipment?: Ensure safe access and fall protection; extend the ladder ≥3 ft above the edge.
First action on entering an electrical panel?: De-energize, lock/tag, and verify absence of voltage with a meter.
What is a SDS (Safety Data Sheet)?: A document describing a chemical/refrigerant's hazards, handling, and first aid.
What is a TXV's job?: A thermostatic expansion valve modulates refrigerant flow to maintain target superheat.
What is a fixed orifice / piston?: A simple metering device with no moving parts; flow varies with pressure difference.
What is flash gas?: A small amount of refrigerant that vaporizes as pressure drops at the metering device.
What is a heat pump (briefly)?: A refrigeration system with a reversing valve so it can heat or cool by moving heat either direction.
What does a reversing valve do?: Switches a heat pump between heating and cooling by reversing refrigerant flow.
Refrigerant in the suction line is?: Low-pressure superheated vapor returning to the compressor.
Refrigerant in the liquid line is?: High-pressure subcooled liquid leaving the condenser.
What is latent heat doing in the evaporator?: Refrigerant boils (changes state) while absorbing heat at nearly constant temperature.
What is latent heat doing in the condenser?: Refrigerant condenses (changes state) while rejecting heat at nearly constant temperature.
Why measure superheat at the evaporator outlet?: To confirm the refrigerant is fully vaporized before it reaches the compressor.
What is MERV?: Minimum Efficiency Reporting Value — a rating of a filter's particle-capture efficiency.
What is a damper?: An adjustable plate that controls airflow in a duct (e.g., balancing or zoning).
What is duct balancing?: Adjusting dampers/registers so each room gets its designed share of airflow.
What is a register vs a grille?: A register has a damper to control airflow; a grille is a fixed-louver cover.
What is the plenum?: The air chamber on the supply or return side of the air handler that distributes air.
Effect of undersized return ducts?: High return static pressure, reduced airflow, and strained equipment.
Why de-energize before measuring resistance?: An ohmmeter applies its own voltage; measuring a live circuit damages the meter and gives false readings.
What is continuity testing?: Checking for a complete (low-resistance) path; used to find open windings, fuses, and switches.
An open circuit reads what resistance?: Infinite (OL) — there is no complete path.
A grounded compressor winding shows?: Low resistance from a winding to the casing (ground) — a failed motor.
Why does voltage drop indicate a bad connection?: A loose/corroded connection adds resistance, dropping voltage and generating heat.
What is inrush (starting) current vs running current?: Inrush is the brief high current at start; running current is the steady draw once up to speed.
What does a sling psychrometer determine?: Relative humidity and dew point (from dry-bulb and wet-bulb readings).
Why does evaporation cool the wet bulb?: Evaporating water absorbs latent heat from the wick, lowering its temperature.
What does a digital psychrometer compute?: RH and dew point from measured dry-bulb and wet-bulb temperatures.
Wet-bulb = dry-bulb means?: The air is fully saturated (100% relative humidity).
Why does humidity ratio use 'grains'?: Grains per pound of dry air is a convenient small unit for water vapor (7,000 grains = 1 lb).
What is enthalpy on the psychrometric chart used for?: Total heat content of the air — basis for total-heat (4.5 × CFM × Δh) calculations.
What is a vapor barrier in construction?: A material that limits moisture migration through walls/floors to prevent condensation.
Why seal duct penetrations through framing?: To prevent air leakage and maintain the building envelope.
What is a soffit?: The underside of an overhang; often used to route ducts and provide intake ventilation.
Why is attic ductwork insulated to a high R-value?: Attics get very hot/cold, so high R-value limits heat gain/loss from the conditioned air.
What is a service valve?: A valve on the system used to connect gauges, charge, or isolate refrigerant during service.
What is a charging scale used for?: Weighing in an exact refrigerant charge for accuracy.
What is a tubing cutter used for?: Making clean, square cuts in copper tubing without crushing it.
What is a reamer/deburring tool for?: Removing burrs from a cut tube end so flow isn't restricted and joints seat properly.
What is a flaring tool?: It forms a 45° cone on a tube end for a mechanical flare fitting.
What does a combustion analyzer measure?: Flue-gas O₂, CO, CO₂, and stack temperature to assess combustion safety and efficiency.
Why is Basic Electricity the heaviest Core area?: It is about 26% of the NATE Core exam — more than any other KATE area.
Two heaviest NATE Core areas?: Basic Electricity (~26%) and Safety (~18%).
Why does a 30 A fuse blow on a normal-draw circuit?: A direct short or a grounded fault is drawing excessive current.

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Click Study Flashcards above to open the flashcard hub — hundreds of NATE HVAC cards you can flip, match, type, or quiz yourself on. Every card is drawn from the seven official NATE Core KATE knowledge areas, so you study exactly what the exam tests.^[1] Pair them with our free practice test and study guide.

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Flip mode turns all 255 cards into quick two-sided review. Match times you on pairing terms with their definitions. Type hides the term and asks you to spell it from the definition alone, so a front like What is superheat? has to come back cold. Quiz builds multiple-choice items from the same cards for a final check.

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Why Flashcards Work for the NATE Exam

Basic Electricity is the largest domain at 61 cards, covering circuit math, motor types, and control hardware. Expect the card that asks Ohm’s law?, along with prompts like PSC vs ECM efficiency? and Contactor vs relay? that force you to separate two similar items quickly.

Using Basic Science follows with 52 cards on refrigeration theory and the vocabulary behind system performance. Cards such as What is superheat? and What is subcooling? anchor the charging concepts, while Boyle’s law (gas)? pushes into the gas behavior you need before you read a single pressure.

Safety holds 36 cards weighted toward refrigerant handling and jobsite hazards, so the card that asks EPA 608 Type I? sits beside prompts like Ladder 4-to-1 rule? and What is arc flash?. Achieving Desired Conditions adds 32 cards on airflow and comfort control, including What is MERV?, What is the plenum?, and the Total heat airflow formula? card.

Tools carries 28 cards on the hardware you handle daily, from the card that asks What is a micron gauge for? to Manifold gauge colors? and What is swaging?. Taking Temperature & Humidity Measurements adds 26 cards on psychrometric readings, with fronts like Wet-bulb depression?, What is relative humidity?, and the card that asks 7,000 grains equal?.

Basic Construction closes the deck with 20 cards on building structure and plan-reading language, the vocabulary that shows up when you size, route, or mount equipment. Look for prompts such as What are joists? and What is a soffit?, plus the card that asks What does R-value measure?.

The NATE exam is dense with facts — Ohm’s law and the power formulas, the refrigeration cycle, fire classes, psychrometric terms, tool functions, and safety rules.^[2] Spaced flashcards are the most efficient way to keep it all fresh. Used alongside our practice test and study guide, they turn review time into measurable progress.

NATE Flashcards by KATE Area

The cards are organized by the seven official NATE Core KATE knowledge areas. Drill the highest-yield ones first — Basic Electricity and Safety carry the most questions on the exam:^[1]

NATE flashcards by KATE knowledge area
Knowledge area	What it covers
Basic Electricity (~26%)	Ohm's law, power, series/parallel, capacitors, contactors, motors
Safety (~18%)	Lockout/tagout, fire classes, PPE, ladders, EPA 608
Achieving Desired Conditions	Comfort, humidity, 400 CFM/ton, airflow formulas, filtration
Temperature & Humidity Measurement	Dry/wet-bulb, dew point, psychrometrics, calibration
Tools	Manifold & micron gauges, vacuum/recovery, brazing, leak detection
Using Basic Science	Refrigeration cycle, heat transfer, sensible/latent, combustion
Basic Construction	Framing, reading plans, ductwork, R-value, hazardous materials

How to Get the Most Out of These Flashcards

Start with Basic Electricity. At 61 cards it is the biggest block, and its motor and circuit vocabulary keeps resurfacing in Tools and Achieving Desired Conditions cards later.
Type-drill the single-word answers. Definitions that resolve to one exact term, like the cards asking What is enthalpy? and What is a hygrometer?, are where typing exposes fuzzy recall fast.
Use Match for lookalike sets. The EPA 608 Type I?, Type II, Type III, and Universal cards in Safety reward fast recognition, and Match trains that pairing under a clock.
Switch to the practice test once recall holds. When Basic Electricity and Using Basic Science come back clean in Quiz, move to the practice test and send misses back to the study guide.
Keep sessions short and rotating. With 255 cards across seven domains, work two domains per sitting, then Flip yesterday’s missed cards before starting anything new.

NATE Flashcards FAQ

Hundreds of free NATE flashcards, organized across all seven KATE knowledge areas — from Basic Electricity and Safety to the refrigeration cycle, psychrometrics, tools, and basic construction. They're free with no account required.

References

1.North American Technician Excellence. “NATE Certification — Core & Specialty Exams.” natex.org. ↑
2.U.S. Environmental Protection Agency. “Section 608 Technician Certification Requirements.” epa.gov. ↑
3.U.S. Department of Energy. “Furnaces and Boilers.” energy.gov. ↑

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