HVAC Electrical Controls and Safety

Question 1

What voltage is typically used for the low-voltage control circuit in a residential HVAC system?

Accepted Answer

24V AC

Answer

Residential HVAC control circuits operate at 24V AC, supplied by a step-down transformer from the 120V or 240V power supply.

Question 2

What is the function of a contactor in an air conditioning system?

Accepted Answer

To switch high-voltage power to the compressor and condenser fan motor

Answer

A contactor is an electrically operated switch that uses a low-voltage coil to close contacts that supply high-voltage power to the compressor and condenser fan.

Question 3

What does a capacitor do in an HVAC motor circuit?

Accepted Answer

Stores electrical energy to help start and run single-phase motors

Answer

Capacitors store electrical energy and create a phase shift that provides starting torque and improves running efficiency in single-phase HVAC motors.

Question 4

What is the purpose of a disconnect switch near an outdoor HVAC unit?

Accepted Answer

To provide a local means of de-energizing the unit for safe service work

Answer

The disconnect switch allows service technicians to safely de-energize the outdoor unit locally without going to the main electrical panel, as required by OSHA and NEC.

Question 5

What does a high-pressure switch in a refrigeration system do?

Accepted Answer

Shuts down the compressor if refrigerant pressure exceeds a safe limit

Answer

The high-pressure switch is a safety device that opens and shuts off the compressor if discharge pressure rises above a safe setpoint, preventing equipment damage.

HVAC - Heating, Ventilation, and Air Conditioning Practice Test

HVAC - Heating, Ventilation, and Air Conditioning Practice Test

HVAC Electrical Controls and Safety