313D Electrical Systems and Controls 5

Question 1

A residential heat pump defrost control board initiates defrost based on:

Accepted Answer

Time and temperature, or time and pressure, depending on board design

Answer

Most defrost boards use a time-and-temperature or time-and-pressure strategy to determine when frost buildup warrants a defrost cycle.

Question 2

On a residential AC system, what is the role of the low-voltage common wire (C-wire) connected to the thermostat?

Accepted Answer

To complete the 24V circuit by providing a return path to the transformer secondary

Answer

The C-wire is the common terminal of the 24V transformer secondary, completing the circuit for thermostat operation and smart thermostat power.

Question 3

What type of electrical fault would cause a ground fault circuit interrupter (GFCI) to trip on an AC circuit?

Accepted Answer

Current leaking from a hot conductor to ground exceeding ~5 mA

Answer

A GFCI detects an imbalance between hot and neutral (or ground path) current as small as 4–6 mA, indicating current is leaking to ground through an unintended path.

Question 4

A residential condenser fan motor runs in the wrong direction after replacement. The MOST likely cause is:

Accepted Answer

The start and run capacitor leads were swapped on the new motor

Answer

Swapping the start winding leads relative to the run winding reverses the phase shift and changes motor rotation direction.

Question 5

What does it mean when a contactor shows pitted or burned contact surfaces?

Accepted Answer

The contacts have experienced arcing and should be replaced to prevent unreliable operation

Answer

Pitted contacts result from electrical arcing during switching, which degrades contact surface quality and increases resistance, leading to heat buildup and potential failures.

(313D) Residential Air Conditioning Systems Mechanic Certification Practice Test

(313D) Residential Air Conditioning Systems Mechanic Certification Practice Test

313D Electrical Systems and Controls 5