313D Electrical Components and Wiring 2

Question 1

What is the purpose of a start capacitor in a single-phase AC compressor motor?

Accepted Answer

Provide a phase shift to boost starting torque

Answer

A start capacitor creates a phase shift in the start winding current, producing the torque needed to overcome inertia and start the motor.

Question 2

Which wire color is designated as the common conductor in a standard residential thermostat wiring scheme?

Accepted Answer

Blue or Black (C)

Answer

The C (common) wire, typically blue or black, completes the 24V control circuit by providing the return path to the transformer secondary.

Question 3

A residential air conditioning system uses a 240V/24V step-down transformer. If the primary side shows 240V but the secondary shows 0V, the MOST likely cause is:

Accepted Answer

Open primary winding or blown fuse

Answer

An open primary winding or a blown fuse on the primary side will prevent current flow and result in zero secondary voltage output.

Question 4

What is the standard voltage range for the low-voltage control circuit in residential HVAC equipment?

Accepted Answer

24V AC

Answer

Residential HVAC control circuits operate at 24V AC, supplied by the system transformer, to power thermostats, relays, and contactors.

Question 5

A contactor coil measures infinite resistance with an ohmmeter. This indicates the coil is:

Accepted Answer

Open and will not energize

Answer

Infinite resistance on a coil indicates an open circuit, meaning no current can flow through the coil and the contactor will not pull in.

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

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

313D Electrical Components and Wiring 2