FREE 313D Electrical Schematics and Controls Questions and Answers

Question 1

On a residential air conditioning schematic, what is the function of a contactor?

Accepted Answer

To use a low-voltage signal to switch the high-voltage power to the compressor and condenser fan motor.

Answer

To step down high voltage to low voltage for the control circuit.

Answer

To protect the system from operating in dangerously low or high refrigerant pressure conditions.

Answer

To control the speed of the indoor blower motor based on the thermostat setting.

Question 2

A technician is troubleshooting a system where the indoor fan runs continuously, but the outdoor unit never starts. A multimeter shows 24V at the thermostat's 'Y' terminal when calling for cooling, but the contactor coil is not energized. Which of the following is the MOST likely cause?

Accepted Answer

A tripped high-pressure safety switch.

Answer

A faulty run capacitor for the compressor.

Answer

A failed indoor blower motor.

Answer

The thermostat is improperly configured.

Question 3

While examining a wiring diagram, you see a symbol representing a switch that is held open by a spring and closes when a magnetic field is created by a coil. This symbol most likely represents which of the following components?

Accepted Answer

A normally open (NO) relay.

Answer

A circuit breaker.

Answer

A transformer.

Answer

A thermostatic expansion valve.

Question 4

A technician is diagnosing a no-cool situation. The thermostat is calling for cooling, and the low-voltage fuse on the indoor unit's control board is blown. What is a common cause for this issue?

Accepted Answer

A short circuit in the low-voltage wiring between the indoor and outdoor units.

Answer

A clogged air filter.

Answer

An overcharged refrigerant system.

Answer

A stuck-closed contactor.

Question 5

In a residential AC electrical schematic, which component is responsible for protecting the compressor from damage if there is a refrigerant leak causing suction pressure to drop to an unsafe level?

Accepted Answer

The low-pressure switch.

Answer

The run capacitor.

Answer

The high-pressure switch.

Answer

The circuit breaker.

Question 6

On a schematic, the thermostat wires are typically represented by which of the following?

Accepted Answer

Thin, solid lines connecting low-voltage components like the thermostat, control board, and contactor.

Answer

Heavy, solid lines indicating high voltage.

Answer

Dotted lines connecting to the refrigerant piping.

Answer

A single line labeled 'COMM' for communication.