NATE Electrical and Controls

Question 1

What is the standard line voltage for most residential HVAC equipment in the United States?

Accepted Answer

240V/60Hz

Answer

Most residential HVAC equipment in the US operates on 240V single-phase 60Hz power.

Question 2

Which component in an HVAC control circuit is used to sense thermostat demand and energize the compressor contactor?

Accepted Answer

Control relay

Answer

A control relay receives the low-voltage thermostat signal and switches the higher-voltage circuit to energize the compressor contactor.

Question 3

What does the label 'R' on an HVAC thermostat terminal typically represent?

Accepted Answer

24V AC power from the transformer

Answer

The 'R' terminal supplies 24V AC power from the control transformer to the thermostat and control circuit.

Question 4

A single-phase motor fails to start and hums loudly. Which component is MOST likely the cause?

Accepted Answer

Start capacitor

Answer

A failed start capacitor prevents the phase shift needed for starting torque, causing the motor to hum without starting.

Question 5

What is the purpose of a high-pressure cutout switch in an HVAC system?

Accepted Answer

Protect the compressor from excessive discharge pressure

Answer

A high-pressure cutout switch opens the control circuit when discharge pressure exceeds a safe limit, protecting the compressor from damage.

NATE - North American Technician Excellence Practice Test