Previous NATE AC Service Practice Test 3 Next NATE AC Service Practice Test 5

NATE_AC_SERVICE NEC 2023

NATE AC Service Practice Test 4

This test covers compressor types, motor types, and starting components used in residential AC systems. You will practice identifying scroll, reciprocating, and rotary compressors, plus capacitor and motor basics.

TOPICS COVERED

NATE AC Service

How this test works

Read each question carefully

Look for absolute words like always / never — they often distinguish the right answer.

Manage your time

You have 30 min for 30 questions. Skip tough ones and come back.

Progress is auto-saved

Your answers are saved locally — a page refresh won't lose your work.

Review your answers

After submitting you'll see every explanation and your NEC references.

Frequently Asked Questions

Yes — completely free with no signup required. Every question includes a full explanation of the correct answer.

Two: the NATE Core exam plus at least one specialty exam (for example AC Service, Heat Pump Service, or Air Distribution Service). You can take them on the same day or separately.

The Core exam has 50 questions and each installation or service specialty exam has 100 questions. You need 70% on each to pass — 35 of 50 on Core and 70 of 100 on a specialty. Check natex.org for the current format before you book.

NATE certification lasts two years. To renew, you submit 16 hours of continuing education or retake the specialty exam before your certification expires.

No. These are independent practice tests written to match the published NATE exam topics. They are not official NATE exam questions.

Exam Tip: Capacitors hold a dangerous charge even after power is off. Always discharge one safely with an insulated tool before touching its terminals.

30

Questions

30 min

Time

70%

Pass

Timer starts immediately. Progress is auto-saved.

NATE AC Service Practice Test 4 — Question List

Question 1: Which compressor type is most commonly used in residential AC systems today?

Scroll compressor
Screw compressor
Centrifugal compressor
Axial compressor

Question 2: How does a reciprocating compressor compress refrigerant?

With pistons moving up and down inside cylinders
With two interleaving spiral scrolls
With a rotating impeller at high speed
With a magnetic field only, no moving parts

Question 3: What is a general feature of a rotary compressor?

It floods the evaporator with liquid refrigerant by design
It uses a rotating mechanism inside a cylinder to compress refrigerant
It only operates on three-phase power
It has no compression chamber at all

Question 4: What does PSC stand for in an AC motor, and where is it commonly used?

Permanent Split Capacitor, used on condenser fan and blower motors
Positive Series Circuit, used only on compressors
Pressure Sensing Control, used on pressure switches
Power Supply Converter, used on control boards

Question 5: What does a run capacitor do on a PSC motor?

It disconnects the motor completely once it reaches full speed
It only assists for the first half-second, then disconnects
It stays in the circuit while running, helping create the needed phase shift
It controls the thermostat setpoint

Question 6: Why do some compressors use a start capacitor in addition to a run capacitor (CSIR or CSCR configurations)?

To provide extra starting torque needed under load
To reduce voltage to the compressor permanently
To slow the compressor down during startup
To replace the need for a contactor

Question 7: True or False: A start capacitor typically stays in the circuit only briefly during start-up and then is switched out, usually by a relay.

False, start capacitors always stay in the circuit continuously
False, start capacitors are never switched out
True
False, only run capacitors are switched out

Question 8: What is a typical acceptable tolerance range for a run capacitor's rated microfarad (MFD) value?

Roughly plus or minus 6 percent
Roughly plus or minus 50 percent
Exactly 0 percent, no tolerance allowed
Roughly plus or minus 25 percent

Question 9: Why must a capacitor be safely discharged before a technician handles its terminals, even after the power is turned off?

A capacitor can retain a dangerous charge even with power off
Capacitors are always completely safe once power is off
It is only a concern for start capacitors, not run capacitors
It is only a concern in commercial equipment

Question 10: What is a "dual run capacitor" commonly used for in residential condensing units?

It replaces the contactor entirely
It is only used for indoor blower motors
It provides run capacitor function for both compressor and condenser fan motor
It stores backup power for the thermostat

Question 11: A compressor hums but does not start, and then trips its overload. What is a common cause to check first?

A dirty air filter
A programmed thermostat schedule
A weak or failed run capacitor
Low indoor humidity

Question 12: What is the difference between SEER and EER as efficiency ratings for AC equipment?

SEER and EER measure the exact same thing with different units
EER measures seasonal efficiency; SEER measures one rated condition
SEER measures seasonal efficiency; EER measures one rated condition
Neither rating relates to compressor efficiency

Question 13: With the unit running, a run capacitor carries 5.2 amps with 345 volts across its terminals. Using µF = (2,652 × amps) ÷ volts, what is its actual capacitance?

About 66 µF
About 13.9 µF
About 1.5 µF
About 40 µF

Question 14: What is the function of the contactor in an outdoor condensing unit?

It measures refrigerant pressure
It stores refrigerant during defrost
It regulates indoor humidity
It is a switch connecting line voltage power to the compressor and fan

Question 15: How are low-pressure and high-pressure safety switches typically wired in relation to the contactor coil circuit?

In parallel, closing to start the compressor on high pressure
In series, but only active during heating mode
They are not connected to the contactor circuit at all
In series, as normally closed switches that open on unsafe pressure

Question 16: In standard thermostat wiring conventions, what does the "Y" terminal typically control?

The 24V hot power supply
The cooling call that energizes the contactor
The indoor blower fan only, with no connection to cooling
The common wire for the transformer

Question 17: A compressor starts normally but its running amp draw is well above the nameplate rated load amps (RLA). What should the technician check?

Refrigerant charge, airflow, and head pressure
The compressor's locked rotor amp rating
The contactor coil voltage
The indoor humidity sensor only

Question 18: A run capacitor is rated 45 µF ±6%. Which measured value means it should be replaced?

43.0 µF
46.8 µF
41.5 µF
45.0 µF

Question 19: What does a potential relay do in a CSIR or CSCR compressor starting circuit?

It controls indoor blower speed only
It senses motor speed and switches the start capacitor out once near full speed
It measures refrigerant subcooling
It replaces the need for a run capacitor

Question 20: What is a "hard start kit" used for on a PSC compressor?

It reduces the compressor's running voltage permanently
It replaces the contactor with a solid-state relay
It converts a three-phase compressor to single-phase
It adds a start capacitor and relay for extra starting torque

Question 21: A technician notices a run capacitor with a bulging or domed top. What does this usually indicate?

The capacitor is operating at peak performance
The capacitor is failing and should be replaced
The capacitor needs more refrigerant charge
The capacitor has too much capacitance and is overpowering the motor

Question 22: Between PSC and CSCR (capacitor-start, capacitor-run) compressor motors, which one generally provides higher starting torque?

PSC, because it has no start capacitor to slow it down
They are always identical in starting torque
CSCR, because it uses both a start and run capacitor together at start-up
Neither type has any starting torque difference by design

Question 23: True or False: A run capacitor that has weakened and reads well below its rated microfarad value can cause a motor to overheat, run slower, or fail to start.

False, capacitor value has no effect on motor performance
False, only start capacitors can cause these symptoms
False, a weak capacitor only affects noise, never performance
True

Question 24: A compressor has an internal overload protector. What is its purpose?

It senses excessive motor temperature or current and opens the circuit to protect the compressor
It increases refrigerant pressure to boost capacity
It controls the indoor thermostat display
It is only found on condenser fan motors, never compressors

Question 25: Where are rotary compressors most commonly found?

Only in large commercial chillers
In smaller equipment such as window units and mini-splits
Only in industrial ammonia refrigeration systems
They are no longer used in any equipment

Question 26: What is the correct order of steps before testing a run capacitor with a multimeter?

Test it first, then turn off power afterward
Turn off power, discharge the capacitor, then test it
Discharge it while power is still on
Skip discharging since testing is quick

Question 27: A single-phase compressor's terminals read: 1 to 2 = 4.0 ohms, 1 to 3 = 0.8 ohms, 2 to 3 = 3.2 ohms. Which terminal is Common?

Terminal 1
Terminal 3
Terminal 2
It cannot be determined without a wiring diagram

Question 28: A technician finds a dirty condenser coil causing high head pressure, along with a compressor drawing high amps. What is the most likely relationship between these two findings?

The two findings are unrelated coincidences
The compressor amp draw is causing the head pressure to rise
High head pressure from restricted airflow is making the compressor work harder
A dirty condenser coil always lowers compressor amp draw

Question 29: True or False: A three-phase compressor motor generally does not need a start or run capacitor to start and run, unlike a typical single-phase residential compressor.

False, three-phase motors need even more capacitors than single-phase
False, three-phase power does not exist in HVAC equipment
False, capacitors are required on all compressor types equally
True

Question 30: A three-phase compressor's supply reads 230, 236, and 224 volts. What is the voltage imbalance?

About 5.2 percent
About 1.0 percent
About 2.6 percent
About 12 percent

EXAM CARD NATE_AC_SERVICE

Questions30

Time limit30 min

Pass score70%

Code editionNEC 2023

DifficultyIntermediate

Last reviewedJun 2026

Timer starts immediately. Progress is auto-saved.

Source: NEC 2026 (NFPA 70)