Electrical Schematics and Controls Flashcards
7 cards from real 313D practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Electrical Schematics and Controls flashcards as text
What is the purpose of a transformer in the residential AC control circuit?
Answer: To step down 240V line voltage to 24V for the low-voltage control circuit
The control transformer steps down 240V (or 120V) line voltage to 24V AC, which powers the thermostat and control circuit components safely.
A run capacitor shown in a schematic is connected in series with which motor winding?
Answer: Start winding (auxiliary winding)
The run capacitor is wired in series with the start (auxiliary) winding to create a phase shift that maintains running torque and efficiency in single-phase motors.
When reading a pictorial wiring diagram, a wire shown going to a splice or junction with a dot indicates:
Answer: An electrical connection between crossing or meeting wires
A solid dot at a wire junction on a schematic indicates an electrical connection is made at that point, as opposed to wires that cross without a dot (no connection).
In a residential AC system, the 'G' terminal on the thermostat controls:
Answer: The indoor blower fan relay
The G terminal sends a 24V signal to energize the indoor blower fan relay, allowing the fan to run independently for ventilation without calling for cooling or heating.
What does a solid triangle or arrow symbol on a schematic pointing into a wire or component indicate?
Answer: Direction of conventional current flow or signal direction
An arrow or triangle on a schematic indicates the direction of conventional current flow or the direction of a signal, helping trace circuit operation.
A crankcase heater shown in an AC schematic is typically wired to be:
Answer: Energized continuously when the unit is powered off to keep refrigerant from migrating into the compressor oil
The crankcase heater stays on when the compressor is off to keep the oil warm and prevent liquid refrigerant from accumulating in the crankcase, which would cause compressor damage on startup.
In troubleshooting with a schematic, if voltage is present on both sides of a normally closed safety switch, what does this indicate?
Answer: The switch has opened (tripped) and is blocking current flow to the load
Voltage on both sides of an open switch (with load connected) indicates the switch contacts are open — voltage is present at the input but cannot pass through to the output.