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

120V AC

Answer

12V DC

Answer

48V DC

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

To sense outdoor temperature and adjust the setpoint

Answer

To regulate refrigerant pressure in the system

Answer

To control the low-voltage thermostat circuit

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

Converts AC power to DC power for the control board

Answer

Reduces voltage to the motor during startup

Answer

Measures current draw for the motor protection circuit

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

To manually switch the system between heating and cooling modes

Answer

To protect the unit from voltage spikes and surges

Answer

To connect the thermostat wiring to the outdoor unit

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

Increases compressor speed when system pressure is too high

Answer

Opens the expansion valve to relieve high pressure

Answer

Measures and displays the condensing pressure

Question 6

What is the purpose of a time-delay relay (TDR) in an HVAC control circuit?

Accepted Answer

To introduce a time delay in circuit operation, such as preventing immediate compressor restart

Answer

To delay the thermostat signal to prevent short cycling

Answer

To time the defrost cycle intervals

Answer

To delay the start of the inducer motor