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NATE_HEATPUMP_SERVICE NEC 2023

NATE Heat Pump Service Practice Test 2

This practice test covers the O-type and B-type reversing valve conventions, how to diagnose reversed heating/cooling operation, and basic solenoid coil electrical testing. You will also see questions on thermostat wiring mistakes and how defrost interacts with the O/B convention.

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NATE Heat Pump Service

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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: Never assume a heat pump is O-type or B-type. Always confirm using that specific unit's wiring diagram before wiring or troubleshooting the reversing valve circuit.

30

Questions

30 min

Time

70%

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NATE Heat Pump Service Practice Test 2 — Question List

Question 1: What do the terms "O-type" and "B-type" refer to in a heat pump system?

Two different refrigerant types used in heat pumps
Two different conventions for which mode energizes the reversing valve
Two sizes of outdoor unit
Two brands of thermostats

Question 2: In an O-type heat pump system, when is the reversing valve energized?

In heating mode
Only during defrost
In cooling mode
Only when emergency heat is on

Question 3: In a B-type heat pump system, when is the reversing valve energized?

In cooling mode
Only during defrost
Only when the compressor is off
In heating mode

Question 4: How should a technician determine whether a specific heat pump is O-type or B-type?

Check that unit's own wiring diagram; never assume
Guess based on the brand name
Assume all heat pumps are O-type
Ask the homeowner

Question 5: A thermostat is configured for a B-type reversing valve, but it is actually connected to an O-type system. What is the likely result?

No effect; the system will work normally
The system's heating and cooling modes will run backward
The compressor will refuse to start at all
The outdoor fan will run continuously

Question 6: True or False: Every heat pump manufacturer uses the same O/B convention.

True, it's a fixed industry-wide standard
True, but only for residential units
False, it depends on the specific equipment
False, only commercial units vary

Question 7: Which statement is most accurate about the O-type convention?

It is used on all heat pumps without exception
It was replaced by B-type on all new equipment
It only applies to commercial equipment
It is the more common convention in the US, but should still be verified per unit

Question 8: What actually determines whether a piece of heat pump equipment is O-type or B-type?

How the manufacturer designed the unit's control board and reversing valve circuit
The outdoor temperature at the installation site
The thermostat brand installed
The refrigerant charge level

Question 9: A thermostat offers both O and B terminal options for the reversing valve output. How should a technician decide which one to use?

Pick whichever wire is a certain color
Match the setting to what the outdoor unit's wiring diagram specifies
Use O in summer and B in winter
It does not matter; either works the same

Question 10: A technician wires a thermostat for O-type operation onto a heat pump that is actually B-type, without changing any settings. What will likely happen?

The unit will run in cooling mode nonstop no matter the call
The unit will not power on at all
The unit will heat when the thermostat calls for cooling, and cool when it calls for heating
The unit will run defrost nonstop

Question 11: True or False: The reversing valve solenoid is energized in both heating and cooling mode at the same time.

True, it must always stay energized to work
True, but only during moderate weather
False, it is never energized in either mode
False, it is energized in only one of the two modes, depending on convention

Question 12: What actually decides whether the O or B output is energized on a given call for heating or cooling?

The heat pump control board or thermostat's programmed mode logic
The size of the compressor
The type of refrigerant in the system
The outdoor unit's paint color

Question 13: Before replacing a failed reversing valve solenoid coil, what should a technician verify?

The color of the old coil's wire insulation
That the replacement coil matches the correct voltage and type for that valve
The age of the compressor
The brand of thermostat installed

Question 14: A homeowner gets a new thermostat installed, and afterward the heat pump cools the house when set to heat. What is the most likely cause?

The compressor is undersized
The outdoor coil is dirty
The new thermostat's O/B setting does not match this system's convention
The refrigerant charge is low

Question 15: True or False: Most residential heat pumps sold in the US use the O-type convention, but a technician should still confirm this for each specific unit.

False, most use B-type
False, the convention does not exist
True, and it never needs to be confirmed
True, and it should still be confirmed per unit

Question 16: What is the most reliable source for confirming whether a heat pump is O-type or B-type?

The unit's own wiring diagram or manufacturer documentation
The color of the outdoor unit's cabinet
The thermostat's brand name
The technician's past experience with a different brand

Question 17: A technician wants to test a reversing valve solenoid coil for continuity using a multimeter. What reading indicates the coil is likely good?

Zero resistance exactly
A measurable resistance value within the coil's normal range, not open or shorted
Infinite resistance
The meter reading does not matter

Question 18: A reversing valve solenoid coil tests as infinite resistance (open circuit) on a multimeter. What does this mean?

The coil is functioning normally
The coil is shorted
The coil is likely burned out and needs replacement
The refrigerant charge is low

Question 19: A reversing valve solenoid coil tests at 0 ohms (or very close to it) on a multimeter, well below its normal rating. What does this suggest?

The coil is in perfect working condition
The coil is open
The compressor is short-cycling
The coil winding may be shorted

Question 20: True or False: Accidentally swapping the O and B wiring connections at the thermostat can reverse which mode energizes the valve.

True
False, O and B wiring cannot be swapped
False, this only affects the outdoor fan
False, this only matters during defrost

Question 21: What voltage do most residential reversing valve solenoid coils typically operate on?

240 volts
24 volts (low-voltage control circuit)
480 volts
120 volts directly from the disconnect

Question 22: A reversing valve solenoid buzzes or chatters when energized instead of shifting cleanly. What should a technician suspect?

The refrigerant type was recently changed to a higher-pressure blend
The thermostat display needs replacement
Possible low or unstable control voltage, or a weak/failing coil
The condensate drain is clogged

Question 23: True or False: A technician should assume every heat pump is O-type unless told otherwise.

True, because O-type is required by code
True, because B-type no longer exists
True, since B-type is only used overseas
False, always verify using that unit's documentation

Question 24: What is a best practice before finishing a thermostat replacement on an existing heat pump system?

Confirm the O/B convention setting matches the outdoor unit before finishing the swap
Always default the new thermostat to B-type
Skip checking the old wiring since new thermostats self-detect the convention
Remove the reversing valve before starting

Question 25: What does an O/B setting (switch or menu option) on a heat pump thermostat actually do?

It adjusts the compressor's running speed
It tells the thermostat which terminal to energize for the connected equipment's convention
It changes the color of the display backlight
It sets the outdoor fan cycling schedule

Question 26: During a defrost cycle, which state does the reversing valve go to, regardless of whether the system is O-type or B-type?

It stays in whatever position matches the heating convention
It moves to a neutral, de-energized middle position
It temporarily moves to whichever state corresponds to cooling mode, since defrost runs the system in cooling briefly
It shuts off completely until defrost ends

Question 27: True or False: Knowing a heat pump's O/B convention only matters for cooling mode, not heating mode.

True, heating mode never involves the reversing valve
True, since heating mode is always the default
True, but only on B-type systems
False, it matters for correct operation in both modes

Question 28: Why should a technician avoid relying only on wire color to identify O and B connections?

Wire colors can vary between manufacturers and installations, so the wiring diagram is the reliable source
Wire colors are standardized worldwide and never vary
Wire color has no relationship to any wiring at all
O and B wires are always the same color as the compressor wire

Question 29: A technician measures 24 volts present at the reversing valve solenoid terminals during a call for cooling, but the valve does not shift and the coil tests with normal resistance. What should be checked next?

The thermostat display brightness
Whether the valve itself has a mechanical (stuck slide) problem, since voltage and coil appear fine
The size of the electrical disconnect
The outdoor unit's paint condition

Question 30: Which of these correctly summarizes the O/B convention concept?

O and B always mean the exact same thing on every heat pump
O-type and B-type only affect the outdoor fan motor, not the reversing valve
O-type energizes the valve in cooling mode, B-type energizes it in heating mode, and the correct one must be confirmed per unit
Only commercial heat pumps use O-type or B-type conventions

EXAM CARD NATE_HEATPUMP_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)