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NATE_AC_SERVICE NEC 2023

NATE AC Service Practice Test 8

This test covers electrical diagnostics specific to AC systems, including the contactor, pressure safety switches, thermostat wiring, and capacitor safety procedures.

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NATE AC 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: Low and high pressure switches are normally closed safety interlocks wired in series with the contactor coil. Either one opening stops the compressor.

30

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30 min

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70%

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NATE AC Service Practice Test 8 — Question List

Question 1: What does the contactor do in the outdoor condensing unit?

It measures refrigerant subcooling
It regulates blower motor speed
It switches line voltage power to the compressor and fan
It stores backup charge for the thermostat

Question 2: How are the low-pressure and high-pressure safety switches typically wired relative to the contactor coil?

In parallel, closing to energize the coil on unsafe pressure
They are wired directly to the compressor windings, bypassing the coil
In series, but normally open, so they must close to run
In series, normally closed, so either one opening stops the compressor

Question 3: In standard thermostat wiring, what does the "R" terminal represent?

The 24V hot power supply from the transformer
The cooling call output
The common wire for the transformer
The fan call output

Question 4: In standard thermostat wiring, what does the "C" terminal represent?

The cooling call output
The common wire completing the 24V circuit
The high-voltage hot wire
The heating call output

Question 5: A homeowner reports the outdoor unit runs continuously, even after the thermostat is set well above room temperature so cooling should be off. What should the technician suspect?

A blown low-voltage fuse
A weak run capacitor
A stuck (welded) contactor not opening without a call
Low refrigerant charge

Question 6: A technician checks the contactor coil terminals during a cooling call and finds no 24V present. What should be checked next, working back toward the thermostat?

The indoor air filter only
The refrigerant charge level only
The condenser coil cleanliness only
The low-voltage wiring, transformer, and any safety switches in the coil circuit

Question 7: Before touching a capacitor's terminals, even with the power off, what safety step must a technician always take?

Safely discharge the capacitor using an insulated tool
Immediately touch both terminals with bare hands to test it
Skip discharging since power is already off
Submerge the capacitor in water before handling

Question 8: A compressor repeatedly trips its internal overload protector shortly after starting. Amp draw at start-up is measured much higher than normal. What electrical component should be checked first?

The high-pressure switch
The run capacitor (and start components if equipped)
The condensate drain line
The liquid line filter drier

Question 9: True or False: A blown low-voltage fuse on the indoor control board can prevent the contactor from ever being energized, even if everything else is working correctly.

False, low-voltage fuses have no effect on the contactor
False, the contactor operates independently of any control fuse
True
False, this only applies to high-voltage fuses

Question 10: A technician finds the low-voltage fuse blown again shortly after replacing it. What is a likely underlying cause to check?

The condenser fan blade is bent
The air filter is dirty
The refrigerant charge is low
A short circuit in the thermostat wiring or a grounded coil

Question 11: Before working inside the outdoor unit's electrical compartment, what should a technician do first for safety?

Turn off and verify power is off at the disconnect using a meter
Assume power is off without checking
Start working immediately to save time
Only check for power after finishing the repair

Question 12: In standard thermostat wiring conventions, what does the "G" terminal control?

The cooling call to the contactor
The indoor blower fan call
The 24V hot power supply
The common return wire

Question 13: What test can a technician perform with a megohmmeter to check for a grounded compressor motor winding?

A refrigerant subcooling test
A duct static pressure test
An insulation resistance test between compressor terminals and the shell
A capacitor microfarad test

Question 14: True or False: A compressor with a completely open (broken) winding will typically not hum or attempt to start at all, since there is no complete electrical path.

False, an open winding always causes loud humming
False, open windings have no effect on starting
False, this only applies to three-phase compressors
True

Question 15: A single-phase compressor has three terminals labeled Common, Start, and Run. How can a technician identify which terminal is Common using an ohmmeter?

Common is identified as the terminal shared by the two smaller resistance readings
Common is always the terminal with the highest resistance reading
Common cannot be identified without a wiring diagram
Common is always the terminal in the center of the terminal block

Question 16: What does a voltage drop test across a wire connection or contact help identify?

The refrigerant charge level
Excessive resistance at the connection, from corrosion or a loose terminal
The indoor humidity level
The compressor displacement rating

Question 17: A technician finds badly burned and pitted contacts on a contactor. What problem can this cause even if the contactor is still functioning?

It has no effect as long as the unit still runs
It always improves electrical contact over time
Increased resistance causing overheating and possible future failure
It only affects the indoor thermostat display

Question 18: Why does a technician compare a running compressor's measured amp draw to its nameplate rated load amps (RLA)?

Amp draw has no relation to nameplate ratings
Nameplate ratings only apply to indoor blower motors
RLA is only used to select the correct thermostat
To check whether the compressor is within its normal electrical range

Question 19: What is the purpose of the outdoor disconnect switch near a condensing unit?

It allows power to be safely shut off for service near the unit
It regulates refrigerant flow to the evaporator
It measures compressor superheat
It controls indoor blower fan speed only

Question 20: A potential relay's normally closed contacts fail to open after start-up, leaving the start capacitor connected continuously. What is the likely result?

Nothing happens, start capacitors are designed for continuous use
The start capacitor can overheat and fail from continuous duty
The compressor will run more efficiently long-term
The relay will automatically repair itself

Question 21: Why is it good practice to label or photograph wiring before disconnecting components during electrical troubleshooting?

It is only useful for the customer's records, not the technician
It has no practical benefit and wastes time
It helps ensure correct reconnection and avoid miswiring
It is required only on new construction, never on repairs

Question 22: A technician adds several new low-voltage accessories to a system and now the control transformer keeps failing. What is a likely cause?

The thermostat brand is incompatible with any transformer
The refrigerant charge is affecting the transformer
The condenser fan capacitor caused the transformer failures
The added accessories may exceed the transformer's VA rating, overloading it

Question 23: True or False: Some high-pressure switches are auto-reset, closing again once pressure returns to a safe level, while others require manual reset.

True
False, all pressure switches are auto-reset only
False, all pressure switches require manual reset only
False, pressure switches do not reset at all once tripped

Question 24: A system's control board shows intermittent faults and resets randomly. What electrical condition should be checked as a possible cause?

Low refrigerant charge
A poor ground connection or unstable line voltage supply
The type of air filter installed
The blower wheel balance

Question 25: A technician tests a suspect run capacitor with a multimeter's capacitance setting and reads a value far below the rated MFD printed on the capacitor. What should be done?

Leave it installed since it is still producing some capacitance
Add refrigerant to compensate for the weak capacitor
Replace it with a new capacitor of the correct rating
Bypass the capacitor entirely with a jumper wire

Question 26: The indoor blower fan runs continuously, even with the thermostat fan setting on "Auto" and no active call for heating or cooling. What is a likely cause?

Low refrigerant charge
A dirty condenser coil
A weak run capacitor on the compressor
A stuck fan relay or miswired G circuit

Question 27: Why should a technician use a properly rated multimeter (with an appropriate CAT safety rating) when testing HVAC electrical circuits?

A properly rated meter reduces shock and arc-flash risk for that circuit
CAT ratings only indicate the meter's accuracy
All multimeters are rated identically regardless of price
CAT ratings only matter for three-phase industrial equipment

Question 28: A unit nameplated 208/230 V is running on a supply that measures 180 volts. What should the technician conclude?

It is below the typical 187 V minimum (208 V minus 10%) and must be corrected
The voltage is normal, since it is within 10% of 230 volts
The unit will simply run more efficiently at lower voltage
Only the condenser fan motor is affected by low supply voltage

Question 29: A manual-reset high-pressure switch keeps tripping. What is the correct professional approach?

Simply hold the switch closed with tape to bypass it permanently
Replace the switch with a jumper wire and ignore the cause
Investigate and correct the underlying cause before resetting the switch
Increase the thermostat setpoint and take no other action

Question 30: A contactor has 24 volts across its coil during a cooling call, but it does not pull in. The coil reads open (infinite resistance). What is the fix?

Replace the thermostat, because it is not sending a signal
Replace the transformer, because 24 volts is too low
Replace the contactor (or its coil), because the coil winding is open
Add refrigerant, because the low-pressure switch has opened

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)