313A Electrical Controls

Question 1

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

Accepted Answer

An electrically operated switch that uses a low-voltage control signal to engage high-voltage power to the compressor and condenser fan motors

Answer

To measure voltage

Answer

To convert AC power to DC

Answer

To protect against lightning strikes

Question 2

What is the purpose of a high-pressure safety switch (cutout) on a refrigeration system?

Accepted Answer

To shut off the compressor if discharge pressure exceeds a safe limit, preventing equipment damage or rupture

Answer

To regulate the normal operating pressure

Answer

To increase the pressure for faster cooling

Answer

To control condenser fan speed

Question 3

What is the purpose of a run capacitor on a compressor motor?

Accepted Answer

To improve the efficiency and power factor of the motor by creating a phase shift in the run winding during normal operation

Answer

To store backup power for outages

Answer

To start the motor spinning

Answer

To regulate voltage to the motor

Question 4

What is the difference between a start capacitor and a run capacitor?

Accepted Answer

A start capacitor provides high torque during motor startup and disconnects via a relay; a run capacitor stays in the circuit continuously to improve efficiency

Answer

They are identical and interchangeable

Answer

A start capacitor is larger; a run capacitor is smaller

Answer

Start capacitors are used only in heating; run capacitors only in cooling

Question 5

What is a thermostat and how does a programmable thermostat save energy?

Accepted Answer

A temperature-sensing control that activates heating or cooling; a programmable thermostat saves energy by automatically adjusting setpoints based on schedules (setback during unoccupied periods)

Answer

A switch that only turns on heating

Answer

A device that measures humidity only

Answer

A safety device that prevents overheating

Question 6

What is a transformer in an HVAC control circuit and what voltage does it typically provide?

Accepted Answer

It steps down line voltage (240V or 120V) to 24V AC to power the thermostat and control circuit safely

Answer

It converts 24V to 240V for the compressor

Answer

It converts AC to DC for electronic controls

Answer

It boosts voltage during brown-out conditions