313D Electrical Systems and Controls 3

Question 1

A residential AC system uses a dual run capacitor. Which terminals are typically labeled on this component?

Accepted Answer

C (common), FAN, HERM

Answer

A dual run capacitor has three terminals: C (common), HERM (compressor/hermetic), and FAN (condenser fan motor).

Question 2

What is the function of a hard start kit (potential relay and start capacitor) added to an existing AC compressor?

Accepted Answer

Increase starting torque to help the compressor start under difficult conditions

Answer

A hard start kit adds extra starting torque, which is helpful when supply voltage is low, refrigerant pressures are unequalized, or the compressor is aging.

Question 3

An ECM blower motor in a residential air handler is different from a PSC motor because it:

Accepted Answer

Uses a variable-speed DC motor controlled by an integrated module

Answer

ECM (Electronically Commutated Motor) motors use a built-in inverter and brushless DC technology to vary speed efficiently.

Question 4

When using a clamp-on ammeter to measure compressor current, you clamp around only one power conductor. Why?

Accepted Answer

To measure the current in one leg without cancellation from opposing current flow

Answer

Clamping around both conductors simultaneously causes the opposing magnetic fields to cancel out, resulting in a near-zero reading.

Question 5

A high-pressure switch in a residential AC system is wired in series with the:

Accepted Answer

Compressor contactor coil circuit

Answer

The high-pressure switch opens the control circuit to de-energize the contactor coil, shutting off the compressor when discharge pressure exceeds a safe limit.

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

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

313D Electrical Systems and Controls 3