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HVAC NEC 2023

HVAC Heat Pump Practice Test 4

Free HVAC Heat Pump Practice Test 4. 25 questions covering refrigerant circulation direction, indoor coil as heat transfer surface, O-terminal cooling control, low-pressure gas between evaporator and compressor, heat pump high efficiency advantages, underground heat pump class requirements, voltmeter and thermostat troubleshooting, low-charge reversing valve diagnosis, incorrect thermostat wiring effects, reversing valve operational modes, refrigerant oil types, heat pump electrical safety, defrost board operation, auxiliary heat lockout settings, and refrigerant phase changes.

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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.

Key facts: In cooling mode, refrigerant flows from compressor → outdoor coil (condenser) → metering device → indoor coil (evaporator) → back to compressor. The reversing valve changes the direction for heating. The "O" terminal on the thermostat energizes the reversing valve solenoid when cooling in most systems. Refrigerant between the evaporator outlet and compressor inlet is in a low-pressure gas (vapor) state with some superheat added.

25

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45 min

Time

70%

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HVAC Heat Pump Practice Test 4 — Question List

Question 1: Which of the following substance circulates through heat pump that transfers, absorbs and releases heat?

Water
Refrigerant
Air
Gas

Question 2: Which of the following component of heat pump heat transfer takes place?

Coil
Compressor
Reversing valve
Expansion valve

Question 3: Which of the following terminal is connected if the heat pump is in cooling mode?

O terminal
B terminal
R terminal
B terminal

Question 4: In the compression refrigeration cycle, the pipe between the evaporator and compressor consists of:

A medium temperature, high pressure liquid
Low pressure and low temperature gas
A high pressure , high temperature gas
A high pressure, low temperature liquid

Question 5: Which of the following heating mechanism will have high efficiency?

Gas furnace
Heat pump
Electric heating element

Question 6: Which of the following is not a heat pump class?

Ground type
Air to air type
Water to air type
Direct buried type

Question 7: If there is a voltage reading in voltmeter which is connected across thermostat terminals indicates ……………………

The thermostat terminals open
The thermostat terminals closed
The thermostat is working correctly
The thermostat is shorted

Question 8: In which of the following condition the reversing valve may not shift from heat to cool mode?

Low refrigerant charge
Obstructed outdoor coil
High compressor discharge pressure
Incorrect setting of thermostat

Question 9: Which of the following is the possible cause heat pump not operating?

Incorrect thermostat setting
Low refrigerant charge
Obstructed outdoor coil
No voltage to the coil

Question 10: What is the purpose of reversing valve in heat pump?

Changes the direction of refrigerant
Changes the direction of indoor and outdoor coils
Changes the direction of condenser heat exchange
Changes the direction of compressor motor

Question 11: What type of lubricating oil is required in an R-410A heat pump system?

Mineral oil is required in R-410A systems because it provides the best lubrication at high pressures
Polyolester (POE) oil is required in R-410A systems because it is miscible with HFC refrigerants and compatible with high system pressures
Alkylbenzene (AB) oil is required because it was specifically developed for R-410A heat pumps
Any refrigeration oil can be used in R-410A systems as long as the viscosity rating matches

Question 12: What does the NEC require regarding the electrical disconnect for an outdoor heat pump unit?

The outdoor unit can use the main panel breaker as its only disconnect as long as the panel is in the same building
NEC 440.14 requires a disconnect within sight (within 50 feet, visible) of the outdoor unit that locks open and disconnects all ungrounded conductors
No disconnect is required for heat pump outdoor units under 240V because they are plug-connected
The disconnect must be inside the air handler cabinet for technician convenience

Question 13: What is "demand defrost" on a heat pump and how does it differ from time-temperature defrost?

Demand defrost activates every time outdoor temperature drops below 32°F regardless of coil condition
Demand defrost detects actual frost accumulation before initiating defrost, avoiding unnecessary cycles that waste energy and reduce comfort compared to fixed-timer defrost
Demand defrost and time-temperature defrost are the same — the terms are used interchangeably
Demand defrost requires the user to manually initiate the defrost cycle based on observation of the outdoor unit

Question 14: A customer complains that the auxiliary heat strips are running constantly even when outdoor temperature is above 50°F. What thermostat setting may be incorrectly configured?

Auxiliary heat running above 50°F is normal — the heat pump always needs backup resistance heat
The auxiliary heat lockout temperature is likely set too high; it should be 35-40°F so strips only run when the heat pump genuinely needs supplemental heat
The outdoor unit reversing valve is stuck — replace it to restore normal heat pump heating
The auxiliary heat strips are the correct size for the home — increase the thermostat setpoint temperature

Question 15: Where in the refrigerant circuit does the refrigerant change from liquid to vapor, and where does it change from vapor to liquid?

Refrigerant changes from liquid to vapor in the condenser and from vapor to liquid in the evaporator
In cooling mode, refrigerant evaporates (liquid→vapor) in the indoor evaporator coil absorbing heat, and condenses (vapor→liquid) in the outdoor condenser coil rejecting heat
Refrigerant phase changes only occur at the metering device — the coils maintain constant refrigerant state
Refrigerant changes phase only in the compressor — it remains liquid in coils and vapor in lines

Question 16: A hermetic compressor trips its internal overload repeatedly. After allowing it to cool, it starts but trips again within minutes. What diagnostic tests should be performed?

Keep resetting the overload until it stops tripping — this is a break-in issue in new compressors
Diagnose in order: supply voltage, system pressures (head/suction), run capacitor µF, compressor winding resistance, and ground insulation resistance to identify what is overloading the compressor
Replace the overload protector — it is faulty if it trips in less than 30 minutes of operation
Add refrigerant to lower the head pressure and reduce the overload trips

Question 17: What do the high-side and low-side manifold gauges measure in a heat pump system, and which service valve connects to each gauge?

The high-side gauge connects to the suction line (larger line) to measure low-pressure refrigerant
The high-side (red) gauge connects to the liquid/discharge service port; the low-side (blue) gauge connects to the suction line port. From these pressures, condensing and evaporating temperatures are determined
Both gauges connect to the same service port — one measures pressure and the other measures temperature
The manifold gauge set is only used in charging mode — do not connect it during normal operation

Question 18: What is the function of the contactor in a heat pump outdoor unit and what symptoms indicate a faulty contactor?

The contactor is a safety device that shuts off the system if refrigerant pressure gets too high
The contactor is an electrically-operated switch controlled by 24V that connects 240V to the compressor and fan; welded contacts cause continuous operation, burned contacts cause voltage drop, and open coil prevents startup
The contactor provides overcurrent protection — it trips like a breaker when amperage is too high
The contactor is not used in heat pump systems — only in air conditioning units

Question 19: What are the approved methods for detecting refrigerant leaks in an HFC heat pump system, and which is most sensitive?

Only soap bubble solution can be used to detect HFC leaks — electronic detectors are prohibited by EPA
Approved methods include electronic detectors, UV dye, nitrogen/bubble tests, and ultrasonic detection; electronic heated-diode detectors are the most sensitive, capable of detecting leaks as small as 0.1 oz/year
The only approved method for HFC leak detection is complete refrigerant recovery followed by nitrogen pressurization
HFC leaks are undetectable without laboratory analysis of the refrigerant — field testing is not possible

Question 20: How is subcooling measured in a heat pump, and what does abnormally high subcooling indicate?

Subcooling is measured on the suction line and normal value is 8-12°F
Subcooling = condensing temperature − liquid line temperature; measured at the liquid line. High subcooling (>25°F) indicates overcharge or liquid line restriction
Subcooling should always be zero — any subcooling indicates the condenser is performing poorly
Subcooling measurement requires specialized equipment only available to manufacturer service technicians

Question 21: Why has the scroll compressor largely replaced the reciprocating (piston) compressor in residential heat pumps?

Scroll compressors are being phased out because reciprocating compressors are more efficient for heat pump applications
Scroll compressors have fewer moving parts, no valves, quieter operation, higher efficiency, better liquid tolerance, and longer life compared to reciprocating piston compressors
Scroll compressors replaced reciprocating types only because they use less refrigerant charge
Scroll compressors can only be used in cooling mode — heating mode still requires reciprocating compressors

Question 22: How does a heat pump address indoor air quality compared to a gas furnace, and what accessories can improve IAQ when used with a heat pump?

Heat pumps produce more indoor air pollutants than gas furnaces due to the refrigerant chemicals released
Heat pumps have no combustion byproducts (CO, NOx); they recirculate indoor air — ERV/HRV for fresh air, media filters, UV lamps, and dehumidifiers improve IAQ
Heat pumps provide automatic fresh air ventilation because outdoor air flows through the system during heating mode
Indoor air quality is not affected by the type of heating system — only the air filter matters

Question 23: What checks should be performed when commissioning (start-up testing) a newly installed heat pump system?

Commissioning only requires verifying the thermostat reaches setpoint within 30 minutes
Commissioning verifies electrical parameters, refrigerant pressures, superheat/subcooling, indoor airflow, both operating modes, and proper thermostat staging
A new heat pump does not require commissioning — the factory pre-charges and tests the system
Commissioning is only needed for commercial systems — residential heat pumps are self-commissioning

Question 24: A customer switches their heat pump thermostat to "Emergency Heat" mode. What happens and when is this appropriate?

Emergency Heat runs the compressor at maximum capacity along with the heat strips for maximum heating
Emergency Heat bypasses the compressor entirely and runs only resistance strips — appropriate only when the heat pump has failed, not for routine cold weather operation
Emergency Heat operates the heat pump in heating mode regardless of the outdoor temperature, overriding the defrost control
Emergency Heat is a summer mode that bypasses the reversing valve for faster cooling

Question 25: What safety precautions must be followed when handling R-410A refrigerant cylinders?

R-410A cylinders can be stored in hot vehicles during summer because the cylinder is designed for high temperatures
R-410A cylinders must be stored upright in cool areas, never exceed 125°F, use only pressure-rated R-410A hoses/gauges, and never use direct heat to raise cylinder pressure
Empty R-410A cylinders are safe to discard in regular trash because they contain no pressure
R-410A cylinder pressure is the same as R-22, so existing R-22 equipment can safely be used

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 limit45 min

Pass score70%

Code editionNEC 2023

DifficultyIntermediate

Last reviewedJun 2026

Timer starts immediately. Progress is auto-saved.

Source: NEC 2026 Art. 440 & electrical theory