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 an anti-short-cycle timer integrated into a modern AC control board?
Answer: To enforce a minimum off-time between compressor starts to protect it from pressure equalization issues
An anti-short-cycle timer ensures the compressor remains off for a minimum period (typically 3–5 minutes) before restarting, allowing refrigerant pressures to equalize and preventing motor damage.
In a schematic, what does a variable resistor (potentiometer) symbol indicate about a component?
Answer: The component's resistance can be adjusted, such as a fan speed control
A potentiometer symbol (resistor with an arrow) indicates an adjustable resistance, commonly used in fan speed controls, thermostat anticipators, or sensor calibration circuits.
Which terminal on a residential heat pump thermostat controls the reversing valve for switching between heating and cooling modes?
Answer: O or B
The O or B terminal controls the reversing valve solenoid; O energizes the valve in cooling mode (most brands), while B energizes it in heating mode (Rheem/Ruud).
A pressure transducer shown in an AC schematic differs from a pressure switch in that it:
Answer: Provides a continuously variable analog or digital output proportional to the refrigerant pressure
A pressure transducer outputs a variable signal (voltage or current) proportional to pressure, allowing precise monitoring, while a pressure switch only has an open/closed output at a fixed setpoint.
In a residential AC ladder diagram, each horizontal 'rung' of the ladder represents:
Answer: An individual control circuit path from power to neutral (or common)
Each rung of a ladder diagram is a complete control circuit path showing the series/parallel arrangement of contacts and coils between the two power rails (L1 and L2/Neutral).
What type of motor protection device is shown as a bimetallic strip symbol in a compressor circuit schematic?
Answer: Internal overload protector (klixon)
A bimetallic strip symbol represents the internal overload protector (commonly called a klixon), which opens the circuit when the compressor motor windings overheat.
When a schematic shows a relay coil labeled 'IFR' (Indoor Fan Relay) with its associated contacts shown elsewhere in the diagram, the contacts will be labeled:
Answer: IFR with a number suffix to indicate which contact set they belong to
Contacts associated with a relay coil use the same label as the coil (IFR) plus a number suffix (IFR-1, IFR-2) to show which relay controls those contacts, allowing technicians to trace the circuit.