HVAC Electrical Controls and Safety 2

Question 1

What color is the common wire (C-wire) in a standard HVAC thermostat wiring scheme?

Accepted Answer

Blue or Black

Answer

Red

Answer

White

Answer

Green

Question 2

In a standard thermostat wiring system, what does the 'Y' terminal control?

Accepted Answer

The compressor/cooling call

Answer

The furnace heat call

Answer

The fan-only operation

Answer

The second stage heat

Question 3

What type of motor is most commonly used for HVAC variable-speed blowers in high-efficiency systems?

Accepted Answer

ECM (Electronically Commutated Motor)

Answer

Single-phase induction motor

Answer

DC shunt motor

Answer

Universal motor

Question 4

What is the purpose of a lockout/tagout (LOTO) procedure in HVAC service?

Accepted Answer

To isolate and de-energize equipment to prevent accidental startup during maintenance

Answer

To lock the thermostat setpoint during unoccupied hours

Answer

To lock refrigerant valves during transport

Answer

To tag equipment that needs repair for the next service call

Question 5

What does a sequencer do in an electric furnace?

Accepted Answer

Staggers the energization of multiple heating elements to prevent large current spikes

Answer

Sequences the compressor stages in a cooling system

Answer

Controls the order of heating and cooling during changeover

Answer

Sequences the zone valves in a hydronic system

Question 6

What happens when a flame sensor in a gas furnace is coated with oxidation or debris?

Accepted Answer

The furnace ignites but shuts down after a few seconds on lockout

Answer

The furnace runs continuously without shutting off

Answer

The gas valve opens further to compensate

Answer

The inducer motor speeds up to improve combustion