NATE (North American Technician Excellence) Certification — Questions and Answers

Question 1: What condition does a very high return static pressure typically indicate?

Excessive supply air
Restricted return airflow due to clogged filter, blocked return grilles, or undersized return duct (Correct answer)
Oversized ductwork
Refrigerant overcharge

Correct answer: Restricted return airflow due to clogged filter, blocked return grilles, or undersized return duct

High return static pressure means the system is starved for return air, which reduces airflow and increases strain on the blower.

Question 2: What is the recommended method for charging a heat pump system in heating mode?

Charge by sight glass clarity
Charge by outdoor ambient temperature chart
Charge by subcooling measured at the outdoor coil liquid line (Correct answer)
Charge by suction superheat at the indoor coil

Correct answer: Charge by subcooling measured at the outdoor coil liquid line

In heating mode, the outdoor coil is the condenser, so subcooling at the outdoor liquid line is the correct charging method.

Question 3: What is the purpose of a liquid line solenoid valve in a refrigeration system?

Control condensing fan speed
Stop refrigerant flow to the evaporator when the thermostat is satisfied or during pump-down (Correct answer)
Regulate refrigerant pressure in the liquid line
Prevent liquid refrigerant from returning to the compressor

Correct answer: Stop refrigerant flow to the evaporator when the thermostat is satisfied or during pump-down

A liquid line solenoid valve closes on a thermostat-off signal, stopping refrigerant flow and allowing the compressor to pump down the evaporator.

Question 4: What does ACCA Manual D provide for HVAC installations?

Commissioning and startup procedures
Equipment selection guidelines
Procedures for residential duct system design and sizing (Correct answer)
Indoor air quality standards

Correct answer: Procedures for residential duct system design and sizing

Manual D provides the calculations and procedures for designing duct systems that deliver the correct airflow to each room based on Manual J loads.

Question 5: What component in an induced-draft furnace proves that combustion airflow is established before the gas valve opens?

Thermocouple
Rollout switch
Limit switch
Pressure switch (Correct answer)

Correct answer: Pressure switch

The pressure switch senses negative pressure created by the inducer motor to confirm draft is established before allowing ignition.

Question 6: What does superheat measure in a refrigeration system?

Temperature rise of vapor above the saturation point at a given pressure (Correct answer)
Compressor discharge temperature
Subcooling at the condenser outlet
Temperature of liquid refrigerant leaving the condenser

Correct answer: Temperature rise of vapor above the saturation point at a given pressure

Superheat is the number of degrees the refrigerant vapor temperature exceeds the saturation temperature at that pressure.

Question 7: What MERV rating range is recommended for residential HVAC filters to balance filtration and airflow?

5–8 (Correct answer)
14–16
9–13
1–4

Correct answer: 5–8

MERV 5–8 filters provide adequate filtration for residential equipment while maintaining sufficient airflow and avoiding excessive pressure drop.

Question 8: What is the primary safety device that shuts off the gas valve if the pilot flame is extinguished on a standing pilot furnace?

Limit switch
Flame sensor rod
Pressure switch
Thermocouple (Correct answer)

Correct answer: Thermocouple

The thermocouple generates a small millivolt signal that holds the gas valve open; when the pilot goes out the signal drops and the valve closes.

Question 9: A heat pump's outdoor unit is making a hissing noise and the reversing valve solenoid is energized. What is the most likely cause?

Reversing valve internal bypass (leaking internally) (Correct answer)
Defrost board failure
Overcharged refrigerant system
Refrigerant leak at the reversing valve

Correct answer: Reversing valve internal bypass (leaking internally)

An internally leaking reversing valve allows high-pressure refrigerant to bypass to the low-pressure side, causing a hissing sound.

Question 10: What is the primary reason refrigerant recovery is required before opening a sealed refrigeration system?

To check refrigerant purity
To reduce system pressure for safe service
To comply with EPA Section 608 and prevent refrigerant release into the atmosphere (Correct answer)
To remove moisture from the circuit

Correct answer: To comply with EPA Section 608 and prevent refrigerant release into the atmosphere

EPA Section 608 prohibits knowingly venting refrigerants; recovery captures refrigerant before system access.

Question 11: What condition is indicated when an air conditioner's evaporator coil is heavily iced over?

High indoor humidity
Excessive outdoor ambient temperature
System is overcharged with refrigerant
Low airflow or low refrigerant charge (Correct answer)

Correct answer: Low airflow or low refrigerant charge

Restricted airflow or low refrigerant charge causes the evaporator to drop below freezing, leading to ice formation.

Question 12: Which wire color in a standard NEC-compliant 120V residential wiring system is the grounded conductor (neutral)?

Red
Black
White (Correct answer)
Green

Correct answer: White

Per NEC, white (or gray) is the grounded conductor (neutral) in a standard 120V residential wiring system.

Question 13: What does the ASHRAE 62.2 standard address in residential applications?

Duct system design procedures
Ventilation and acceptable indoor air quality for residential buildings (Correct answer)
Duct leakage limits for new construction
Minimum equipment efficiency ratings

Correct answer: Ventilation and acceptable indoor air quality for residential buildings

ASHRAE 62.2 specifies minimum mechanical ventilation rates to maintain acceptable indoor air quality in residences.

Question 14: What annual maintenance item is most critical for oil burner efficiency?

Replacing the transformer
Replacing the nozzle and cleaning the strainer, electrodes, and heat exchanger (Correct answer)
Flushing the oil tank
Adjusting the thermostat anticipator

Correct answer: Replacing the nozzle and cleaning the strainer, electrodes, and heat exchanger

An annual tune-up including nozzle replacement and cleaning ensures complete combustion, maximum efficiency, and safe operation.

Question 15: What type of duct fitting causes the most turbulence and pressure drop?

Square elbow without turning vanes (Correct answer)
Long-radius elbow
Conical reducer
Straight section

Correct answer: Square elbow without turning vanes

Sharp square elbows cause severe turbulence and high pressure drop; long-radius elbows or elbows with turning vanes greatly reduce this loss.

Question 16: What is the purpose of the vent pressure switch on a two-stage condensing furnace?

Confirm the inducer is operating at proper speed and the vent is clear before allowing ignition (Correct answer)
Control secondary heat exchanger temperature
Monitor return air static pressure
Verify combustion air is being supplied

Correct answer: Confirm the inducer is operating at proper speed and the vent is clear before allowing ignition

The vent pressure switch proves adequate draft by sensing the negative pressure created by the inducer blower before the gas valve is energized.

Question 17: What does a cracked heat exchanger in a gas furnace risk introducing into the living space?

Nitrogen dioxide only
Carbon monoxide (CO) and other combustion byproducts (Correct answer)
Natural gas from the supply line
Refrigerant vapor

Correct answer: Carbon monoxide (CO) and other combustion byproducts

Cracks in the heat exchanger allow combustion gases including deadly carbon monoxide to mix with circulated air and enter the living space.

Question 18: What component in an oil burner atomizes the fuel oil and mixes it with air for combustion?

Oil pump
Nozzle (Correct answer)
Cad cell
Electrodes

Correct answer: Nozzle

The nozzle atomizes oil into a fine spray at a precise angle and pattern, mixing it with combustion air for efficient burning.

Question 19: Which type of compressor uses scroll technology and is common in modern residential AC units?

Screw
Scroll (Correct answer)
Reciprocating
Centrifugal

Correct answer: Scroll

Scroll compressors use two interlocking spirals and are favored in residential equipment for efficiency and quiet operation.

Question 20: A technician finds a blown fuse in the control circuit. After replacing it, the fuse blows again immediately. What is the BEST next step?

Install a higher-rated fuse
Restart the system immediately
Check for short circuits or grounded wiring in the control circuit (Correct answer)
Replace the transformer

Correct answer: Check for short circuits or grounded wiring in the control circuit

A repeatedly blown fuse indicates a short circuit or grounded wire in the control circuit that must be located and repaired.

Question 21: What percentage of CO2 in flue gas typically represents near-ideal combustion for a #2 oil burner?

8–10%
15–17%
11–13% (Correct answer)
5–7%

Correct answer: 11–13%

CO2 levels of 11–13% indicate near-stoichiometric combustion with minimal excess air and good efficiency for #2 fuel oil.

Question 22: What does the term 'MCA' (Minimum Circuit Ampacity) indicate on an HVAC nameplate?

Maximum fuse size allowed
Maximum current the equipment can draw under any condition
Motor locked-rotor amperage
Minimum wire ampacity required for branch circuit conductors (Correct answer)

Correct answer: Minimum wire ampacity required for branch circuit conductors

MCA specifies the minimum ampacity that the branch circuit conductors must be rated to safely carry for the equipment.

Question 23: What does the label 'R' on an HVAC thermostat terminal typically represent?

Reversing valve signal
24V AC power from the transformer (Correct answer)
Return air sensor
Refrigerant charge indicator

Correct answer: 24V AC power from the transformer

The 'R' terminal supplies 24V AC power from the control transformer to the thermostat and control circuit.

Question 24: What is the function of the delayed oil valve (solenoid valve) on some oil burners?

Allow oil to flow only on a call for heat
Stop oil flow immediately on burner shutdown to prevent after-drip and after-fire (Correct answer)
Prevent oil flow during power outages
Regulate oil pressure during high-fire mode

Correct answer: Stop oil flow immediately on burner shutdown to prevent after-drip and after-fire

The delayed oil valve closes instantly when the burner shuts off, preventing oil drip into the combustion chamber that could cause after-fire and smoke.

Question 25: What is the typical evaporator TD (temperature difference) used to assess evaporator performance in a refrigeration system?

Difference between discharge and suction pressures in degrees
Difference between condensing temperature and ambient
Difference between return air temperature and saturated suction temperature in the evaporator (Correct answer)
Difference between supply and return air temperatures

Correct answer: Difference between return air temperature and saturated suction temperature in the evaporator

Evaporator TD is the difference between the air entering the coil and the saturated suction temperature, indicating heat transfer efficiency.

Question 26: What does a TXV (thermostatic expansion valve) use to control refrigerant flow?

Condenser outlet temperature
Liquid line subcooling
Suction line superheat sensed by a bulb (Correct answer)
Discharge pressure

Correct answer: Suction line superheat sensed by a bulb

A TXV senses evaporator outlet superheat via a sensing bulb and adjusts flow to maintain a set superheat.

Question 27: What is the purpose of the heat exchanger in a gas furnace?

Regulate gas pressure to the burners
Transfer heat from combustion gases to the circulating air without mixing them (Correct answer)
Mix combustion gases with supply air
Remove moisture from combustion products

Correct answer: Transfer heat from combustion gases to the circulating air without mixing them

The heat exchanger keeps combustion products separated from conditioned air while allowing heat transfer through the metal walls.

Question 28: When measuring AC voltage with a multimeter, what type of reading does a standard digital multimeter display?

Average voltage
Peak voltage
Peak-to-peak voltage
RMS (root mean square) voltage (Correct answer)

Correct answer: RMS (root mean square) voltage

Standard digital multimeters display RMS voltage, which represents the effective value of AC voltage equivalent to DC.

Question 29: What condition does a high CO2 reading combined with a high smoke number indicate on a combustion analysis?

Low oil pump pressure
Perfect combustion efficiency
Too little combustion air (rich mixture causing incomplete combustion) (Correct answer)
Too much combustion air (lean mixture)

Correct answer: Too little combustion air (rich mixture causing incomplete combustion)

High CO2 with high smoke indicates insufficient air, producing a rich mixture with incomplete combustion and carbon soot.

Question 30: What type of venting is required for a 96% AFUE condensing gas furnace?

Masonry chimney with liner
Category IV stainless steel vent
PVC plastic pipe for both flue and combustion air (Correct answer)
Type B double-wall vent

Correct answer: PVC plastic pipe for both flue and combustion air

High-efficiency condensing furnaces produce cool, moist flue gases that must be exhausted through PVC pipe; Category IV designation.

Question 31: What is the AFUE rating and what does it measure for a gas furnace?

Annual Fuel Utilization Efficiency; measures what percentage of fuel energy is converted to heat (Correct answer)
Average Furnace Unit Efficiency; measures BTU output
Airflow Factor Under Extreme conditions
Annual Flue Utilization Effectiveness

Correct answer: Annual Fuel Utilization Efficiency; measures what percentage of fuel energy is converted to heat

AFUE expresses as a percentage how much of the fuel's energy is converted to usable heat; a 96% AFUE furnace wastes only 4% up the flue.

Question 32: What does a low suction pressure reading typically indicate in a residential AC system?

Low refrigerant charge or restricted airflow (Correct answer)
Overcharge of refrigerant
Faulty discharge valve
Condenser fan failure

Correct answer: Low refrigerant charge or restricted airflow

Low suction pressure usually points to insufficient refrigerant or reduced evaporator airflow causing lower evaporating temperatures.

Question 33: LP (propane) gas manifold pressure for residential furnaces is typically set to which value?

0.5 PSI
7–11 inches WC (Correct answer)
10–14 inches WC
3.5 inches WC

Correct answer: 7–11 inches WC

Propane furnaces require higher manifold pressure than natural gas, typically 10–11 inches WC, because propane has different combustion characteristics.

Question 34: What does COP (Coefficient of Performance) measure for a heat pump?

Seasonal energy efficiency ratio
Ratio of heat output to electrical energy input (Correct answer)
Compressor displacement volume
Cooling capacity in BTUs

Correct answer: Ratio of heat output to electrical energy input

COP is the ratio of heat energy delivered to electrical energy consumed; a COP of 3 means 3 units of heat per 1 unit of electricity.

Question 35: What is the purpose of the accumulator in a heat pump system?

Regulate condenser airflow
Remove non-condensables from the refrigerant
Store excess refrigerant charge
Prevent liquid refrigerant from entering the compressor (Correct answer)

Correct answer: Prevent liquid refrigerant from entering the compressor

The accumulator is located on the suction line and traps liquid refrigerant, allowing only vapor to reach the compressor.

Question 36: Which EPA section requires technicians to be certified before purchasing refrigerants?

Section 302
Section 410
Section 406
Section 608 (Correct answer)

Correct answer: Section 608

EPA Section 608 regulations require HVAC technicians to be certified when purchasing and handling refrigerants.

Question 37: What is the correct method for measuring total external static pressure (TESP) on an air handler?

Average pressures at all supply registers
Measure velocity pressure at the blower inlet
Measure static pressure in the return plenum before the coil and in the supply plenum after the coil, then subtract return from supply (Correct answer)
Measure only at the supply plenum

Correct answer: Measure static pressure in the return plenum before the coil and in the supply plenum after the coil, then subtract return from supply

TESP = supply static pressure minus return static pressure (both measured close to the air handler), giving total system resistance.

Question 38: What is the standard line voltage for most residential HVAC equipment in the United States?

208V/60Hz
277V/60Hz
120V/60Hz
240V/60Hz (Correct answer)

Correct answer: 240V/60Hz

Most residential HVAC equipment in the US operates on 240V single-phase 60Hz power.

Question 39: What refrigerant is most commonly used in modern residential air conditioning systems in the US?

R-134a
R-410A (Correct answer)
R-22
R-404A

Correct answer: R-410A

R-410A replaced R-22 as the standard residential AC refrigerant due to R-22's ozone-depleting properties.

Question 40: What is the purpose of the metering device in a refrigeration circuit?

Filter moisture from the refrigerant
Reduce refrigerant pressure and control flow into the evaporator (Correct answer)
Remove heat from the condenser
Compress the refrigerant

Correct answer: Reduce refrigerant pressure and control flow into the evaporator

The metering device reduces high-pressure liquid refrigerant to low-pressure liquid/vapor, controlling flow into the evaporator.

Question 41: What is the refrigeration effect and how is it calculated?

Heat absorbed in the evaporator; calculated as evaporator outlet enthalpy minus evaporator inlet enthalpy (Correct answer)
Work input to the compressor
Heat gained by subcooling the liquid line
Heat rejected at the condenser; calculated as condenser enthalpy minus compressor inlet enthalpy

Correct answer: Heat absorbed in the evaporator; calculated as evaporator outlet enthalpy minus evaporator inlet enthalpy

The refrigeration effect is the heat absorbed per pound of refrigerant in the evaporator, equal to the enthalpy difference across the evaporator.

Question 42: What does a #2 fuel oil supply line's two-pipe system accomplish compared to a single-pipe system?

Provides redundancy if the primary supply fails
Increases oil flow rate to the burner
Returns unused oil to the tank, preventing vapor lock and allowing the tank to be below the burner (Correct answer)
Filters water from the oil supply

Correct answer: Returns unused oil to the tank, preventing vapor lock and allowing the tank to be below the burner

A two-pipe system continuously circulates oil back to the tank, preventing air and vapor buildup and allowing a below-burner tank installation.

Question 43: At what outdoor temperature do most standard air-source heat pumps reach their balance point?

35–40°F (Correct answer)
40°F
50°F
25°F

Correct answer: 35–40°F

The balance point is typically 35–40°F, where the heat pump output equals the building heat loss and auxiliary heat is not yet needed.

Question 44: What type of ignition system uses a glowing ceramic element to ignite the gas burners in modern furnaces?

Standing pilot
Direct spark ignition
Spark ignition
Hot surface igniter (HSI) (Correct answer)

Correct answer: Hot surface igniter (HSI)

Hot surface igniters heat to approximately 1800–2500°F using electricity to ignite the gas burner, replacing standing pilots.

Question 45: What tool is used to measure air velocity in a duct or at a register?

Manometer
Anemometer or flow hood (Correct answer)
Combustion analyzer
Psychrometer

Correct answer: Anemometer or flow hood

An anemometer measures air velocity in feet per minute (FPM); a flow hood captures total CFM at a register directly.

Question 46: What unit is used to measure duct air leakage during a duct leakage test?

MERV rating
Grains per pound
Inches WC
CFM25 (cubic feet per minute at 25 pascals) (Correct answer)

Correct answer: CFM25 (cubic feet per minute at 25 pascals)

Duct leakage is expressed as CFM25, the airflow escaping through duct leaks when pressurized to 25 pascals above atmospheric pressure.

Question 47: What is the purpose of a high-pressure cutout switch in an HVAC system?

Limit refrigerant charge
Regulate low-side pressure
Monitor suction line temperature
Protect the compressor from excessive discharge pressure (Correct answer)

Correct answer: Protect the compressor from excessive discharge pressure

A high-pressure cutout switch opens the control circuit when discharge pressure exceeds a safe limit, protecting the compressor from damage.

Question 48: At what temperature range does a medium-temperature refrigeration system typically maintain a reach-in display case?

45°F to 55°F
28°F to 40°F (Correct answer)
0°F to 10°F
-10°F to 0°F

Correct answer: 28°F to 40°F

Medium-temperature refrigeration maintains product temperatures between 28°F and 40°F for dairy, deli, and produce applications.

Question 49: When charging a system with R-410A, the refrigerant cylinder should be held in which orientation?

Any position works
Upright for vapor, inverted for liquid (Correct answer)
Upside down
Upright only

Correct answer: Upright for vapor, inverted for liquid

R-410A must be charged as a liquid (cylinder inverted through a valve) to maintain the correct blend ratio.

Question 50: What does the flame sensor do in a modern electronic ignition furnace?

Measures combustion air temperature
Passes a small DC current through the flame to prove ignition and keep the gas valve open (Correct answer)
Controls burner gas pressure
Monitors heat exchanger temperature

Correct answer: Passes a small DC current through the flame to prove ignition and keep the gas valve open

The flame sensor uses flame rectification—the ionized flame allows DC current to flow—proving the burner is lit and preventing gas buildup.

Question 51: What is a common symptom of a stuck reversing valve in the heating position?

System heats normally but will not cool
Outdoor coil ices over in summer
Both A and C (Correct answer)
Compressor short cycles

Correct answer: Both A and C

A reversing valve stuck in heating mode causes the system to heat when cooling is called for, and the outdoor coil may ice in summer because it acts as an evaporator.

Question 52: What is the purpose of a plenum in an HVAC duct system?

Serve as a pressure chamber that distributes or collects air from multiple duct branches (Correct answer)
House the thermostat sensing element
Filter combustion gases from the airstream
Provide combustion air to the furnace

Correct answer: Serve as a pressure chamber that distributes or collects air from multiple duct branches

The supply plenum distributes conditioned air from the air handler to multiple duct branches; the return plenum collects air from return branches.

Question 53: Which tool is used to measure the wet-bulb temperature when evaluating air conditioning performance?

Manifold gauge set
Anemometer
Clamp meter
Sling psychrometer (Correct answer)

Correct answer: Sling psychrometer

A sling psychrometer uses a wet-bulb and dry-bulb thermometer to measure relative humidity and wet-bulb temperature.

Question 54: What is the purpose of a hot gas defrost system in commercial refrigeration?

Melt frost from evaporator coils by circulating hot discharge gas through them instead of using electric heaters (Correct answer)
Reheat supply air after cooling
Prevent condensation on the case glass doors
Warm the compressor oil at startup

Correct answer: Melt frost from evaporator coils by circulating hot discharge gas through them instead of using electric heaters

Hot gas defrost diverts discharge gas from the compressor into the evaporator to melt frost quickly and efficiently without electric heaters.

Question 55: What is the purpose of the oil filter installed in the oil supply line before the pump?

Filter sediment and particulates that could clog the nozzle or damage the pump (Correct answer)
Remove water from the oil
Reduce oil temperature
Control oil flow rate

Correct answer: Filter sediment and particulates that could clog the nozzle or damage the pump

The oil filter traps rust, sediment, and debris from the tank that could plug the fine nozzle orifice or damage pump components.

Question 56: What is a dual-fuel heat pump system?

A heat pump that can use solar and grid electricity
A system with two compressors for redundancy
A heat pump that uses both R-410A and R-32 refrigerants
A heat pump paired with a gas furnace that automatically switches to gas heat below a set outdoor temperature (Correct answer)

Correct answer: A heat pump paired with a gas furnace that automatically switches to gas heat below a set outdoor temperature

Dual-fuel systems use the heat pump for mild weather and switch to the gas furnace when outdoor temperatures drop below the economic balance point.

Question 57: What does HSPF2 measure for a heat pump?

Heating efficiency measured as total heat output divided by total electrical energy over the heating season (Correct answer)
Cooling efficiency over a season
Defrost cycle frequency
Compressor efficiency ratio

Correct answer: Heating efficiency measured as total heat output divided by total electrical energy over the heating season

HSPF2 (Heating Seasonal Performance Factor 2) rates heating efficiency; higher values indicate more efficient heating performance.

Question 58: What refrigerant is used in low-temperature frozen food applications and has an evaporating temperature around -20°F?

R-404A or R-448A (Correct answer)
R-410A
R-22
R-134a

Correct answer: R-404A or R-448A

R-404A and its replacement R-448A are designed for low and medium-temperature commercial refrigeration systems.

Question 59: What does it mean when a refrigeration system has non-condensables present?

Moisture has entered the refrigerant circuit
Refrigerant charge is too low
Gases such as air or nitrogen are trapped in the system and raise head pressure without contributing to refrigeration (Correct answer)
The system is properly charged with nitrogen for leak testing

Correct answer: Gases such as air or nitrogen are trapped in the system and raise head pressure without contributing to refrigeration

Non-condensable gases accumulate in the condenser, raise discharge pressure, reduce capacity, and increase compressor work without transferring heat.

Question 60: What is the minimum SEER2 requirement for a new split-system AC unit installed in the US Southeast after January 1, 2023?

14 SEER2 (Correct answer)
13 SEER2
15 SEER2
16 SEER2

Correct answer: 14 SEER2

The US Department of Energy set the minimum SEER2 efficiency standard at 14 for split systems in the Southeast and Southwest regions effective January 2023.

Question 61: What is the purpose of the electrodes in an oil burner?

Produce a high-voltage spark to ignite the atomized oil-air mixture (Correct answer)
Sense the flame via rectification
Measure flue gas temperature
Control oil pump speed

Correct answer: Produce a high-voltage spark to ignite the atomized oil-air mixture

Electrodes are positioned in the air-oil spray and produce a continuous or intermittent spark to ignite the mixture at startup.

Question 62: What is the recommended insulation R-value for ducts installed in unconditioned attics in most US climate zones?

R-11
R-8 (Correct answer)
R-6
R-4

Correct answer: R-8

Most US energy codes and ACCA guidelines recommend R-8 duct insulation for ducts in unconditioned attic spaces to minimize heat gain or loss.

Question 63: What is the minimum clearance from combustibles required for Type B vent pipe in most residential applications?

6 inches
3 inches
No clearance required
1 inch (Correct answer)

Correct answer: 1 inch

Type B double-wall vent pipe requires only 1-inch clearance from combustible materials due to its insulating outer jacket.

Question 64: What type of compressor is most commonly used in large commercial refrigeration rack systems?

Centrifugal
Reciprocating (semi-hermetic) (Correct answer)
Scroll
Absorption

Correct answer: Reciprocating (semi-hermetic)

Semi-hermetic reciprocating compressors are widely used in commercial rack systems because they are serviceable and available in a wide range of capacities.

Question 65: What outdoor temperature indicates a heat pump may need a 'cold climate' or variable-speed model to remain effective?

Below 32°F
Below 50°F
Below 20°F
Below 0°F (Correct answer)

Correct answer: Below 0°F

Standard heat pumps lose significant capacity below 32°F, while cold-climate models maintain heating capacity down to -13°F or lower.

Question 66: A furnace high-limit switch trips repeatedly. What is the most common cause?

Dirty air filter or restricted airflow causing the heat exchanger to overheat (Correct answer)
Faulty thermostat
Low gas pressure
Gas valve is stuck open

Correct answer: Dirty air filter or restricted airflow causing the heat exchanger to overheat

Restricted airflow from a clogged filter or blocked supply/return prevents adequate heat dissipation, causing heat exchanger temperatures to exceed the limit switch setpoint.

Question 67: What is the correct procedure when a gas leak is suspected at a furnace?

Do not use any electrical switches; leave the building and call the gas company (Correct answer)
Apply pipe dope and continue operating the furnace
Turn on exhaust fans and relight the pilot
Increase gas pressure to identify the leak location

Correct answer: Do not use any electrical switches; leave the building and call the gas company

Any electrical switch operation could ignite accumulated gas; evacuate immediately and contact the gas utility from outside.

Question 68: What is the primary control's 'safety timing' function on an oil furnace?

Prevent the burner from firing more than 3 times per hour
Allow a limited time for ignition then shut down the burner if no flame is proven (Correct answer)
Control circulator pump timing
Purge the combustion chamber before ignition

Correct answer: Allow a limited time for ignition then shut down the burner if no flame is proven

Safety timing (typically 45–90 seconds) limits how long unburned oil can accumulate before locking out the burner to prevent explosion.

Question 69: What is the typical target evaporator superheat range for a fixed-orifice metering device system?

0–5°F
5–10°F
10–18°F (Correct answer)
25–40°F

Correct answer: 10–18°F

A fixed-orifice system typically targets 10–18°F of superheat at the evaporator outlet for proper refrigerant feed.

Question 70: What does external static pressure (ESP) measure in an HVAC duct system?

Return air CO2 concentration
Duct leakage to outside
Velocity of air at the supply registers
Total resistance to airflow the blower must overcome, measured in inches of water column (Correct answer)

Correct answer: Total resistance to airflow the blower must overcome, measured in inches of water column

ESP is the sum of supply and return static pressures and indicates how hard the blower works against the duct system resistance.

Question 71: What is the standard gas manifold pressure for natural gas residential furnaces in the US?

10–12 inches WC
7–14 inches WC
3.2–3.8 inches WC (Correct answer)
0.5–1.0 PSI

Correct answer: 3.2–3.8 inches WC

Natural gas furnace manifold pressure is typically set at 3.2–3.8 inches water column (around 3.5 inches WC nominal).

Question 72: What is the typical oil pump pressure setting for a residential oil burner?

200–300 PSI
100–150 PSI (Correct answer)
25–40 PSI
50–60 PSI

Correct answer: 100–150 PSI

Residential oil burner pumps typically operate at 100–150 PSI (commonly 100 PSI) to properly atomize the fuel through the nozzle.

Question 73: During defrost mode, why does the indoor electric heat strip energize?

To temper the cool air being delivered while the system is in cooling mode for defrost (Correct answer)
To prevent the compressor from overheating
To prevent the outdoor coil from freezing
To boost system capacity in cold weather

Correct answer: To temper the cool air being delivered while the system is in cooling mode for defrost

During defrost the refrigerant cycle reverses to cooling mode, delivering cold air indoors; auxiliary strips energize to prevent occupant discomfort.

Question 74: Which component in an air conditioning system is responsible for rejecting heat to the outdoors?

Condenser (Correct answer)
Compressor
Evaporator
Expansion valve

Correct answer: Condenser

The condenser releases heat absorbed from the indoor air to the outdoor environment.

Question 75: What is the function of a crankcase heater on a compressor?

Warm the discharge line in winter
Increase compressor speed at startup
Prevent refrigerant from migrating into the compressor oil during off cycles (Correct answer)
Heat the outdoor coil to prevent frost

Correct answer: Prevent refrigerant from migrating into the compressor oil during off cycles

Crankcase heaters keep compressor oil warm to prevent refrigerant absorption and potential liquid slugging on startup.

Question 76: A contactor coil is rated at 24V AC. If the supply voltage to the coil drops to 18V AC, what is the MOST likely result?

The contactor opens the circuit
The contactor coil burns out immediately
The contactor operates normally
The contactor may chatter or fail to fully close (Correct answer)

Correct answer: The contactor may chatter or fail to fully close

Insufficient coil voltage prevents full magnetic engagement, causing the contactor to chatter or fail to close completely.

Question 77: What color should the burner flame be on a properly adjusted natural gas furnace?

Mostly blue with slight yellow tips (Correct answer)
Pure white
Red/orange
Yellow/orange with tips

Correct answer: Mostly blue with slight yellow tips

A properly burning natural gas flame should be predominantly blue, indicating complete combustion, with minor yellow tips acceptable.

Question 78: A single-phase motor fails to start and hums loudly. Which component is MOST likely the cause?

Overload protector
Start capacitor (Correct answer)
Contactor
Run capacitor

Correct answer: Start capacitor

A failed start capacitor prevents the phase shift needed for starting torque, causing the motor to hum without starting.

Question 79: What is the purpose of the Schrader valve on a refrigeration system?

Regulates compressor speed
Controls refrigerant flow rate
Provides a service port for pressure measurement and refrigerant access (Correct answer)
Prevents refrigerant from reversing direction

Correct answer: Provides a service port for pressure measurement and refrigerant access

Schrader valves are spring-loaded service ports that allow gauges and charging equipment to connect to the system.

Question 80: Which type of furnace venting uses a dedicated fresh-air intake pipe running alongside the flue pipe?

Power vent system
Direct vent (sealed combustion) system (Correct answer)
Natural draft venting
Type B common vent

Correct answer: Direct vent (sealed combustion) system

Direct vent sealed-combustion furnaces draw all combustion air from outside through a dedicated intake, preventing depressurization of the home.

Question 81: What does a megohmmeter (megger) measure?

Contactor coil impedance
Insulation resistance of motor windings (Correct answer)
AC line frequency
Capacitor microfarad rating

Correct answer: Insulation resistance of motor windings

A megohmmeter applies high DC voltage to measure insulation resistance, revealing breakdown or moisture in motor windings.

Question 82: What is the function of the rollout switch on a gas furnace?

Detect flame rollout and shut down the furnace if heat exceeds safe limits near the burner compartment (Correct answer)
Monitor supply air temperature
Control the inducer motor speed
Measure gas manifold pressure

Correct answer: Detect flame rollout and shut down the furnace if heat exceeds safe limits near the burner compartment

Rollout switches are manual-reset thermal devices that trip if flames exit the burner compartment, indicating a serious combustion problem.

Question 83: Which component in an HVAC control circuit is used to sense thermostat demand and energize the compressor contactor?

Thermistor
Capacitor
Transformer
Control relay (Correct answer)

Correct answer: Control relay

A control relay receives the low-voltage thermostat signal and switches the higher-voltage circuit to energize the compressor contactor.

Question 84: What does a barometric draft control (draft regulator) do in an oil heating system?

Control combustion air to the burner
Boost flue draft in low-pressure conditions
Maintain constant flue draft by admitting dilution air when draft exceeds setpoint (Correct answer)
Prevent flue gases from entering the living area

Correct answer: Maintain constant flue draft by admitting dilution air when draft exceeds setpoint

The barometric damper swings open to admit room air when draft is too strong, maintaining a stable negative pressure in the flue.

Question 85: When a heat pump is in heating mode and the emergency heat is energized, what happens?

Both the compressor and electric strips run simultaneously
The reversing valve switches to cooling mode
The outdoor fan runs at high speed
Only electric resistance strips provide heat; the compressor is locked out (Correct answer)

Correct answer: Only electric resistance strips provide heat; the compressor is locked out

Emergency heat bypasses the heat pump compressor and relies solely on electric resistance heat strips, typically used when the heat pump has failed.

Question 86: What is subcooling in an air conditioning system?

Lowering the thermostat setpoint
Reducing condenser fan speed
Number of degrees liquid refrigerant is cooled below its saturation temperature (Correct answer)
Cooling the suction line below ambient

Correct answer: Number of degrees liquid refrigerant is cooled below its saturation temperature

Subcooling measures how many degrees the liquid refrigerant has been cooled below its condensing saturation temperature.

Question 87: What is a condensate drain trap used for on a high-efficiency furnace?

Reduce drain line vibration
Filter particulates from the condensate water
Trap combustion gases before they exit
Prevent flue gases from backing up through the condensate drain while allowing water to drain freely (Correct answer)

Correct answer: Prevent flue gases from backing up through the condensate drain while allowing water to drain freely

The condensate trap maintains a water seal that blocks furnace gases from escaping through the drain while permitting condensate to flow out.

Question 88: What is the maximum recommended duct velocity for residential supply ducts to minimize noise?

2,000+ FPM
400–600 FPM
700–900 FPM (Correct answer)
1,200–1,500 FPM

Correct answer: 700–900 FPM

Residential supply ducts typically target 700–900 FPM to balance duct size with acceptable noise levels.

Question 89: A high-efficiency split system AC rated at SEER 18 performs better than a unit rated at which of the following?

SEER 21
SEER 16 (Correct answer)
SEER 19
SEER 20

Correct answer: SEER 16

SEER (Seasonal Energy Efficiency Ratio) measures cooling efficiency; higher numbers indicate better efficiency.

Question 90: What annual efficiency rating measures the seasonal performance of an oil furnace?

COP
SEER
AFUE (Correct answer)
EER

Correct answer: AFUE

AFUE (Annual Fuel Utilization Efficiency) measures the percentage of fuel converted to heat over the heating season for oil furnaces.

Question 91: What does a smoke tester (Bacharach pump) measure on an oil burner?

Carbon soot level in flue gases by comparing a filter paper sample to a standard scale (Correct answer)
Combustion air temperature
Oil pump pressure
Stack gas CO2 percentage

Correct answer: Carbon soot level in flue gases by comparing a filter paper sample to a standard scale

The smoke tester draws flue gas through filter paper; the resulting stain is compared to a numbered scale (0 = clean, 9 = heavy smoke).

Question 92: What is the function of the cad cell (cadmium sulfide cell) in an oil burner primary control?

Measure oil pump pressure
Sense the presence or absence of a flame by its resistance to light (Correct answer)
Monitor stack temperature
Control the firing rate of the burner

Correct answer: Sense the presence or absence of a flame by its resistance to light

The cad cell changes resistance based on light; in darkness (no flame) its high resistance signals the primary control to initiate lockout.

Question 93: What is the effect of duct leakage in unconditioned spaces like attics and crawlspaces?

Only affects humidity levels
Has negligible effect on system performance
Slightly increases equipment run time
Wastes significant conditioned air to outside, dramatically increasing energy consumption and reducing comfort (Correct answer)

Correct answer: Wastes significant conditioned air to outside, dramatically increasing energy consumption and reducing comfort

Leaking supply ducts in unconditioned spaces lose conditioned air to outside while leaking return ducts pull hot/cold unconditioned air into the system.

Question 94: What is a bypass damper used for in a zoned duct system?

Relieve excess static pressure when zone dampers close by routing air back to the return side (Correct answer)
Control humidity in a single zone
Balance airflow between supply and return plenums
Provide fresh outdoor air to the return system

Correct answer: Relieve excess static pressure when zone dampers close by routing air back to the return side

When zone dampers close, the bypass damper opens to maintain minimum airflow across the coil and prevent equipment damage from excessive static pressure.

Question 95: What is the recommended duct sealing material for permanent duct repairs?

Standard gray cloth duct tape
Spray foam insulation
Silicone caulk
Mastic sealant or metal foil tape (UL 181 listed) (Correct answer)

Correct answer: Mastic sealant or metal foil tape (UL 181 listed)

Mastic sealant and UL 181 listed foil tape are durable, code-approved methods; standard cloth duct tape dries out and fails over time.

Question 96: What does a lockout/tagout (LOTO) procedure require before servicing electrical HVAC equipment?

Isolating and de-energizing the power source and verifying zero energy state (Correct answer)
Switching the system to cooling mode
Lowering thermostat setpoint to off
Wearing rubber-soled shoes

Correct answer: Isolating and de-energizing the power source and verifying zero energy state

LOTO requires disconnecting and locking the energy source, then verifying zero energy state before any service work begins.

Question 97: What component allows a heat pump to reverse the refrigeration cycle between heating and cooling modes?

Accumulator
Reversing valve (Correct answer)
Thermostatic expansion valve
Check valve

Correct answer: Reversing valve

The reversing valve redirects refrigerant flow so the indoor coil acts as a condenser in heating mode and an evaporator in cooling mode.

Question 98: What is a typical symptom of an overcharged heat pump during cooling mode?

Low suction pressure and high discharge pressure
Low suction pressure and low discharge pressure
High suction pressure and high discharge pressure (Correct answer)
Normal pressures but high superheat

Correct answer: High suction pressure and high discharge pressure

Overcharge floods the evaporator with excess liquid refrigerant, raising suction pressure, and increases condenser load, raising discharge pressure.

Question 99: What is a puffback in an oil heating system?

Excessive combustion air condition
Small backfire explosion caused by igniting accumulated unburned oil in the combustion chamber (Correct answer)
Reverse airflow through the flue
Oil pump pressure surge

Correct answer: Small backfire explosion caused by igniting accumulated unburned oil in the combustion chamber

A puffback occurs when oil mist accumulates before ignition and ignites suddenly, causing a small explosion that can spread soot throughout the home.

Question 100: What is the purpose of a balancing damper in a duct branch?

Prevent backdrafting
Filter particulates from the airstream
Reduce duct noise
Adjust airflow to individual zones to balance the system and deliver correct CFM to each room (Correct answer)

Correct answer: Adjust airflow to individual zones to balance the system and deliver correct CFM to each room

Balancing dampers restrict airflow in over-supplied branches, diverting more air to under-supplied areas for proper room-by-room comfort.

NATE (North American Technician Excellence) Certification

The NATE certification exam validates HVAC technician knowledge and skills across specialty areas including air conditioning, heat pumps, gas heating, oil heating, and air distribution systems. Technicians must demonstrate competency in installation and service/troubleshooting to earn industry-recognized NATE credentials.

100

Questions

150 min

Time Limit

70%

To Pass

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