Previous HVAC Certification Practice Test 19

HVAC NEC 2023

HVAC Certification Practice Test 20

A mixed diagnostic review combining superheat/subcooling readings with electrical fault scenarios — meters, motor nameplate data, safety switches, and anti-short-cycle protection.

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HVAC Practice tests

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Frequently Asked Questions

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

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

Exam Tip: Real troubleshooting often blends refrigerant-side readings with electrical checks — practice thinking across both at once.

25

Questions

25 min

Time

70%

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HVAC Certification Practice Test 20 — Question List

Question 1: A system shows high superheat and the compressor draws a sustained current near its nameplate LRA without settling to RLA. What is likely happening?

This combination is entirely normal and needs no action
The compressor is stalled at locked rotor current and not actually starting, which is a separate issue from the refrigerant-side superheat reading
High superheat always means the compressor windings are grounded
LRA-level current always means the system is overcharged

Question 2: A system has high superheat, low subcooling, and the low-pressure switch has tripped, shutting down the compressor. What single root cause would explain all three symptoms?

An undercharged system (or a significant refrigerant leak)
An overcharged system
A failed run capacitor only
A miswired G terminal

Question 3: A technician clamps around both compressor leads together and reads 0.2A on a unit rated 16A RLA, and concludes the compressor is off. The compressor is actually running. What mistake was made?

Clamping around both conductors of the same circuit, causing their magnetic fields to cancel and give a falsely low reading
The meter was set to measure resistance instead of current
The compressor nameplate must be incorrect
This reading proves the compressor is grounded

Question 4: A furnace fires, runs briefly, then trips its limit switch. A very dirty filter is found. What single underlying issue likely explains this, and could it also have affected the sail switch earlier?

Restricted airflow from the dirty filter — severe enough to eventually trip the limit switch, and possibly marginal enough to have still allowed the sail switch to initially close
The refrigerant charge is definitely the cause
The run capacitor is definitely the cause
The condenser fan motor is definitely the cause

Question 5: A compressor's running current matches its nameplate RLA closely, but a GFCI-protected disconnect keeps tripping. Continuity checks are normal. What tool and test should the technician use next?

A megohmmeter, to check insulation resistance to ground for a grounded winding
A capacitor tester only
A pressure gauge set only
A thermostat wire color chart

Question 6: After a brief power flicker, a customer calls saying the AC "won't turn on" even though it was working fine before. Before assuming a failure, what should be checked first?

Whether enough time has passed for the anti-short-cycle delay to clear
Whether the refrigerant has completely leaked out
Whether the compressor has permanently failed
Whether the ductwork needs to be replaced

Question 7: A TXV system shows normal subcooling but the compressor briefly hits an amp reading near LRA before settling well below RLA. Is the electrical behavior concerning?

Yes, this always indicates a failing compressor
No — a brief spike near LRA settling to a value at or below RLA is normal starting behavior, unrelated to the subcooling reading
Yes, this always means the TXV has failed
No conclusion can be drawn without knowing the thermostat wire colors

Question 8: Before megger-testing a compressor motor, why should a technician also make sure any related run capacitor has been safely discharged first?

A charged capacitor connected to the circuit could interfere with the test or pose a shock hazard during setup
Capacitors never retain any charge under any circumstances
This step is only relevant to three-phase motors
Megger tests are impossible if a capacitor is present anywhere in the building

Question 9: A three-phase scroll compressor was just reconnected after service. It draws a sustained high current and runs hot without building proper pressure. What two things should the technician check, in order?

First verify phase rotation with a meter, since reversed rotation causes exactly this symptom; then re-check pressures once rotation is confirmed correct
Immediately replace the compressor without further checks
Immediately add more refrigerant without further checks
Immediately replace the thermostat without further checks

Question 10: A compressor that sat without power in cold weather is started immediately after power is restored, without the manufacturer-specified wait time. What refrigerant-and-electrical-related risk does this create?

Refrigerant that migrated into the cold oil can flash to vapor on startup, foaming the oil and risking mechanical damage
There is no risk at all in this situation
This only affects the thermostat display
This only affects the outdoor air damper

Question 11: A blower motor with SF 1.0 has been running continuously above its rated horsepower for months due to a duct restriction. What is a reasonable expectation for this motor's service life?

It is likely to wear out or fail sooner than expected due to sustained operation beyond its rated capacity with no margin
Service factor has no bearing on motor life expectancy
The motor will automatically last longer under these conditions
This scenario has no effect since SF only matters at start-up

Question 12: A TXV system shows superheat swinging erratically, and the compressor's running amp draw is also fluctuating noticeably in step with it. What does this pattern suggest?

The TXV may be hunting/malfunctioning, causing the compressor load (and therefore current draw) to vary along with the unstable superheat
This pattern is always caused by a bad thermostat C wire
This pattern is always caused by a tripped limit switch
This pattern has no relationship between the two readings

Question 13: An outdoor GFCI service receptacle near a condensing unit trips whenever it rains. Is this necessarily a sign the condensing unit's electrical system has failed?

Yes, this always means the condensing unit itself has a wiring fault
Not necessarily — it could simply be the GFCI doing its job in response to a wet connection or compromised cord/tool, separate from the unit's own wiring
Yes, this always means the refrigerant charge is wrong
GFCIs cannot be affected by moisture at all

Question 14: Before replacing a run capacitor, what is the correct safety sequence a technician should follow, combining lockout/tagout and capacitor discharge practices?

De-energize and lock/tag the disconnect, verify zero energy with a meter, then safely discharge the capacitor with an insulated tool before removing it
Simply unplug the thermostat and begin work immediately
Short the capacitor with a bare screwdriver as the first step
No precautions are needed since capacitors are always safe once the breaker is off

Question 15: A blower motor's amp draw reads well below its nameplate FLA, and the sail switch never proves airflow. What single underlying cause could explain both symptoms?

A failing blower motor not moving enough air (and drawing less current as a result), or a blower belt/coupling problem preventing proper airflow
The refrigerant charge is always the explanation for this pattern
The compressor contactor is always the explanation for this pattern
The reversing valve is always the explanation for this pattern

Question 16: On a mild day, a rooftop unit's compressor runs constantly at full capacity instead of using outdoor air first. What component would a technician reasonably investigate?

The economizer damper actuator and its control logic, to see if it is failing to open and use available free cooling
The thermostat wire color scheme only
The crankcase heater only
The recovery cylinder fill level

Question 17: A technician's logged megger readings on a compressor have been trending downward over the past three service visits, though still passing. What is a reasonable proactive recommendation to the customer?

Monitor the trend and plan for a possible future compressor replacement, rather than waiting for a sudden failure
Ignore the trend entirely since the reading currently passes
Immediately replace the thermostat instead
Immediately void the equipment warranty

Question 18: A building experiences a brief, noticeable light flicker every time a large rooftop compressor starts. What electrical concept explains this?

The compressor's brief high inrush (LRA) current draw momentarily loading down the supply voltage
This has no relationship to the compressor at all
This always means the building wiring is undersized beyond any acceptable limit
This always means the compressor is grounded

Question 19: A system with confirmed low refrigerant charge (high superheat, low subcooling) also shows the compressor running current below its nameplate RLA. Why might undercharge cause lower-than-normal running current?

With less refrigerant mass flowing through the system, the compressor may be working against a lighter load than normal, drawing less current
Undercharge always increases running current well above RLA in every case
Refrigerant charge has no relationship to compressor current draw
This pattern proves the thermostat is miswired

Question 20: On a system with a variable-speed (ECM/inverter) blower motor, why might a sail switch calibrated for a fixed-speed blower cause nuisance issues at very low blower speed settings?

At a low modulated speed, actual airflow may be lower than what a switch calibrated for full-speed operation expects, even though the system is operating normally
Variable-speed blowers never move any air at all
Sail switches are never used with variable-speed equipment under any circumstances
This scenario is impossible and cannot occur

Question 21: A condenser fan motor's run capacitor tests at 28 MFD against a 35 MFD ±6% rating, and the motor's running amp draw is noticeably above its nameplate FLA. Are these two findings related?

No, capacitor condition and current draw are always unrelated
Yes — a weak capacitor outside tolerance can cause the motor to work harder and draw more current than normal
Yes, but only because the refrigerant charge is definitely also wrong
No, 28 MFD is actually within the acceptable range for this capacitor

Question 22: After reconnecting a three-phase compressor following a repair, what two checks should generally be completed before considering the job finished, based on topics covered in this test series?

Verify correct phase rotation with a meter, and confirm winding insulation is healthy (e.g., via a megger check) if there is any reason to suspect it was disturbed
Neither check is ever necessary after a repair
Only the thermostat wire colors need to be checked
Only the outdoor air damper needs to be checked

Question 23: Why is it valuable for a technician to consider both refrigerant-side readings (superheat/subcooling) and electrical readings (amp draw, voltage) together when diagnosing a system?

Many real-world faults produce related symptoms on both sides, and looking at only one can miss the full picture or the true root cause
Refrigerant-side and electrical readings are always completely unrelated
Only electrical readings are ever useful in real diagnostics
Only refrigerant-side readings are ever useful in real diagnostics

Question 24: A compressor nameplate lists RLA 20A. A technician properly isolates one conductor and measures 31A during steady running operation, well past start-up. What should this prompt the technician to do?

Do nothing further, since any running current is acceptable
Investigate further — a sustained running current well above nameplate RLA is not normal and needs a cause identified
Assume the meter is always wrong in this situation
Assume the nameplate must be misprinted in every such case

Question 25: A system shows low superheat, high subcooling, a compressor running current above nameplate RLA, and normal continuity/megger readings on the windings. What is the most likely explanation tying these findings together?

The system is overcharged, causing the compressor to work harder (higher current) while the windings themselves remain electrically healthy
The compressor windings are definitely grounded despite the normal megger reading
The system is definitely undercharged
The thermostat is definitely miswired

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