HVAC Electrical Controls 2

Question 1

What is the primary function of a contactor in an HVAC system?

Accepted Answer

Switch high-voltage loads using a low-voltage control signal

Answer

A contactor uses a low-voltage coil (typically 24V) to magnetically close contacts that switch high-voltage loads like compressors and condenser fan motors.

Question 2

A potential relay used in a single-phase compressor motor is installed in which circuit?

Accepted Answer

Start winding in parallel

Answer

The potential relay coil is wired in parallel with the start winding and its normally-closed contacts are in series with the start capacitor, opening once back-EMF rises.

Question 3

Which control device opens on a RISE in temperature to protect a heat exchanger from overheating?

Accepted Answer

High-limit switch

Answer

A high-limit switch is a safety device that opens its contacts when temperature rises above a set point, de-energizing the heat source before damage occurs.

Question 4

In a 24V control circuit, the transformer secondary rating is typically:

Accepted Answer

24V / 40 VA

Answer

Most residential HVAC systems use a 24V, 40 VA control transformer to power the thermostat and control components.

Question 5

What happens when a current-sensing overload protector in a compressor motor trips?

Accepted Answer

The condenser fan continues but the compressor stops

Answer

An internal overload protector opens the compressor circuit, stopping the compressor while other components like the condenser fan may remain energized.

HVAC Practice Test

HVAC Practice Test

HVAC Electrical Controls 2