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 function of a hard start kit (potential relay and start capacitor) shown in a schematic?
Answer: To boost starting torque and reduce locked-rotor amperage duration
A hard start kit adds extra capacitance to boost starting torque, allowing the compressor to start under load and reducing the time spent at high locked-rotor amperage.
In a schematic, what does a contactor coil symbol (circle with a letter designation) energize?
Answer: The main power contacts that supply line voltage to the compressor and condenser fan
When the contactor coil is energized by the 24V control circuit, it pulls in the main power contacts that connect line voltage (240V) to the compressor and condenser fan motor.
A low-pressure switch in an AC schematic is wired in series with the control circuit primarily to:
Answer: Shut down the unit if refrigerant loss causes suction pressure to drop below safe limits
A low-pressure switch opens the control circuit if suction pressure drops below a set point, indicating refrigerant loss or other abnormal conditions, shutting down the compressor.
On a residential split-system schematic, which wire color is most commonly used for the 24V 'Y' (cooling) signal from thermostat to air handler?
Answer: Yellow
The Y terminal carries the cooling call signal, and by industry convention this wire is yellow, though actual installations should always be verified against the wiring diagram.
What does a ground fault circuit interrupter (GFCI) monitor in an electrical circuit?
Answer: The difference in current between the hot and neutral conductors
A GFCI monitors the current difference between hot and neutral; if more than ~5mA is detected (indicating a ground fault), it trips and opens the circuit.
Which type of diagram shows the physical location of components and the actual wire routing between them?
Answer: Wiring diagram
A wiring diagram shows the physical layout and actual routing of wires between components, making it useful for installation and troubleshooting in the field.
In AC system controls, what is the role of a defrost control board in a heat pump schematic?
Answer: It initiates and terminates the defrost cycle to clear frost from the outdoor coil
The defrost control board monitors outdoor coil temperature and time, initiating defrost when needed and terminating it when the coil is clear or a time limit is reached.