Previous HVAC Certification Practice Test 15 Next HVAC Certification Practice Test 17

HVAC NEC 2023

HVAC Certification Practice Test 16

This test takes a deeper look at how single-phase motors start — the start winding, run winding, capacitor phase shift, and the centrifugal switch that disconnects the start circuit.

TOPICS COVERED

HVAC Practice tests

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 25 min for 25 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.

HVAC electrical exams cover electrical theory (Ohm's Law, circuits), transformers, single-phase and three-phase motors, control wiring, safety, and troubleshooting.

Requirements vary by state. HVAC technicians typically need EPA 608 certification and may need a separate electrical license for line voltage work.

Exam Tip: A single AC waveform alone cannot start a single-phase motor turning in one direction — that is the whole reason the start winding and capacitor exist.

25

Questions

25 min

Time

70%

Pass

Timer starts immediately. Progress is auto-saved.

HVAC Certification Practice Test 16 — Question List

Question 1: Why can't a single-phase AC motor start turning in one direction using only its main run winding?

A single AC waveform alone does not create a rotating magnetic field by itself
Single-phase motors have no magnetic field at all
Single-phase power is always too low voltage to start any motor
The run winding is physically incapable of carrying current

Question 2: What role does the start winding play in a single-phase motor?

It is physically offset from the run winding and, combined with a capacitor's phase shift, helps create the field needed to start the rotor turning
It carries the full running load once the motor is up to speed
It has no functional purpose and is only for balance
It replaces the need for a run winding entirely

Question 3: What does a capacitor contribute electrically to help a single-phase motor start?

It shifts the phase of current in the start winding relative to the run winding
It converts the motor to true three-phase operation
It has no electrical effect, only mechanical vibration damping
It supplies DC power to the rotor

Question 4: What does a centrifugal switch do on a CSIR or CSCR motor?

It disconnects the start winding/capacitor from the circuit once the motor reaches a certain running speed
It permanently connects the start winding for continuous use
It controls the condenser fan cycling
It regulates refrigerant flow to the evaporator

Question 5: Why must the start winding and start capacitor be removed from the circuit after the motor reaches running speed?

Leaving them in continuously would overheat the start winding, since it is not designed for continuous duty
There is no consequence to leaving the start winding connected permanently
It would cause the run capacitor to charge in reverse
It would immediately trip the equipment grounding conductor

Question 6: Why does a PSC (Permanent Split Capacitor) motor not need a centrifugal switch?

PSC motors have only a run capacitor, which stays connected continuously by design — there is no start winding/capacitor to disconnect
PSC motors do not use any capacitor at all
PSC motors are three-phase and do not need this feature
PSC motors never actually start turning

Question 7: What combination of capacitors does a CSCR (Capacitor Start, Capacitor Run) motor use?

Both a start capacitor and a run capacitor
A run capacitor only, with no start capacitor
Neither a start nor a run capacitor
Three separate run capacitors

Question 8: Why might a compressor requiring high starting torque use a CSCR design rather than a simpler PSC design?

The added start capacitor provides extra starting torque that a PSC motor's single run capacitor alone cannot supply
CSCR motors are always cheaper to manufacture than PSC motors
CSCR motors do not require any capacitor at all
PSC motors cannot legally be used on compressors

Question 9: A CSIR motor's centrifugal switch fails to open once the motor is up to speed, leaving the start winding continuously energized. What is the likely consequence?

Nothing — this is a normal and safe way to run the motor long-term
The start winding overheats and eventually fails since it is not built for continuous duty
The refrigerant charge automatically decreases
The condenser fan will immediately stop

Question 10: A CSIR motor hums but never starts turning, and current stays high without settling. Besides a bad start capacitor, what mechanical component failure could also cause this?

A centrifugal switch or start relay that is not properly engaging the start circuit
The condenser fan motor alone
The thermostat's C wire connection
The outdoor disconnect distance from the unit

Question 11: On larger compressors, what commonly replaces a mechanical centrifugal switch to disconnect the start circuit?

A current-sensing relay or a potential (voltage-sensing) relay
A high-pressure switch
A crankcase heater
A defrost control board

Question 12: What is a general tradeoff of a PSC motor design compared to CSIR/CSCR designs?

PSC motors generally have lower starting torque since they lack a dedicated start winding/capacitor combination
PSC motors always have the highest possible starting torque
There is no torque difference between any of these motor designs
PSC motors cannot run continuously under any load

Question 13: What is the run winding's role once a single-phase motor is up to speed?

It carries the primary current for continuous, normal running operation
It only operates for the first half-second of starting
It has no function once the motor starts
It only functions when the motor is off

Question 14: A PSC condenser fan motor starts and spins, but noticeably slower than normal with a higher-than-expected amp draw. What is a likely cause?

A weak or failing run capacitor no longer providing an adequate phase shift
This is completely normal PSC motor behavior
The centrifugal switch has failed, since PSC motors have one
The crankcase heater is drawing excess current

Question 15: On many single-phase motors, how can rotation direction be reversed?

By swapping the connections to the start winding relative to the run winding, per the manufacturer's wiring diagram
Single-phase motor direction can never be changed under any circumstances
Only by physically flipping the motor upside down
By increasing the supply voltage

Question 16: When checking a single-phase compressor's three terminals (common, start, run) with an ohmmeter, what pattern is generally expected?

The start-to-run resistance should roughly equal the sum of common-to-start and common-to-run resistances
All three terminal-pair readings should always be identical
There is no relationship between these three readings
Only the run winding can be measured at all

Question 17: How does a start capacitor differ in size (MFD) from a run capacitor on the same motor, and why?

Start capacitors are generally much higher MFD than run capacitors, since they only operate briefly and need to deliver a strong momentary phase shift for torque
Start and run capacitors are always the exact same MFD value
Run capacitors are always higher MFD than start capacitors
MFD rating has no relationship to how the capacitor is used

Question 18: When identifying an unlabeled compressor's common, start, and run terminals with an ohmmeter, which terminal typically shows the lowest combined resistance to the other two?

The common terminal
The start terminal always shows the lowest resistance
The run terminal always shows the lowest resistance
All three terminals always show identical resistance

Question 19: If a compressor repeatedly trips on overload shortly after starting, what start-circuit-related cause should be considered?

The start winding/capacitor may not be disconnecting properly after start-up, causing excess current draw
This has nothing to do with the start circuit at all
This always means the refrigerant charge is too low
This always means the thermostat needs replacement

Question 20: True or False: On a PSC motor, the capacitor is in the circuit only during starting, then disconnects.

True
False
Only true on three-phase PSC motors
Only true above 5 horsepower

Question 21: A CSIR compressor starts fine on a cold morning but struggles to start on a hot afternoon when head pressure is higher. What start-circuit component is commonly a suspect in this pattern?

A weakening start capacitor, which may no longer provide enough starting torque under higher-load conditions
The thermostat batteries only
The outdoor disconnect location
The condensate drain line

Question 22: On a PSC motor with no separate start capacitor, what extra job does the single run capacitor have to perform compared to a CSCR motor's run capacitor?

It must also help provide enough phase shift for adequate starting torque, not just efficient running
It has no additional job compared to a CSCR run capacitor
It handles refrigerant metering instead of the TXV
It replaces the need for a contactor

Question 23: Before checking a compressor's start/run/common winding resistances with an ohmmeter, what should the technician confirm first?

The power is off and the circuit is properly de-energized and verified safe
The compressor should remain fully energized during the test
No safety precautions are needed for resistance measurements
Only the thermostat needs to be off, not the disconnect

Question 24: Which single-phase motor type has NO start capacitor and NO centrifugal switch at all?

CSIR
CSCR
PSC (Permanent Split Capacitor)
They all have identical start circuits

Question 25: A CSR compressor hums, draws high current, and will not start. A capacitor meter shows the start capacitor reading 0 MFD. What is the most likely explanation?

The start capacitor has failed open and is providing no starting assist
This reading indicates the capacitor is functioning perfectly
The reading proves the run winding is open
The reading proves the refrigerant charge is too high

Key NEC References for This Test

Article	What It Covers
Art. 440	Air Conditioning Equipment — use nameplate MCA and MOCP, not FLA alone
Art. 430	Motors — general motor rules that Art. 440 modifies

Study Tip: Practice reading ladder diagrams. Trace each rung from L1 to the load: contacts open → circuit dead. Contacts closed → current flows. This is how HVAC electrical troubleshooting works.

EXAM CARD HVAC

Questions25

Time limit25 min

Pass score70%

Code editionNEC 2023

DifficultyIntermediate

Last reviewedJun 2026

Timer starts immediately. Progress is auto-saved.

Source: NEC 2026 Art. 440 & electrical theory