Electrical Systems 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 Systems and Controls flashcards as text
A residential AC system uses a dual run capacitor. Which terminals are typically labeled on this component?
Answer: C (common), FAN, HERM
A dual run capacitor has three terminals: C (common), HERM (compressor/hermetic), and FAN (condenser fan motor).
What is the function of a hard start kit (potential relay and start capacitor) added to an existing AC compressor?
Answer: Increase starting torque to help the compressor start under difficult conditions
A hard start kit adds extra starting torque, which is helpful when supply voltage is low, refrigerant pressures are unequalized, or the compressor is aging.
An ECM blower motor in a residential air handler is different from a PSC motor because it:
Answer: Uses a variable-speed DC motor controlled by an integrated module
ECM (Electronically Commutated Motor) motors use a built-in inverter and brushless DC technology to vary speed efficiently.
When using a clamp-on ammeter to measure compressor current, you clamp around only one power conductor. Why?
Answer: To measure the current in one leg without cancellation from opposing current flow
Clamping around both conductors simultaneously causes the opposing magnetic fields to cancel out, resulting in a near-zero reading.
A high-pressure switch in a residential AC system is wired in series with the:
Answer: Compressor contactor coil circuit
The high-pressure switch opens the control circuit to de-energize the contactor coil, shutting off the compressor when discharge pressure exceeds a safe limit.
What reading would indicate a shorted run capacitor when tested with a capacitance meter?
Answer: Reading of 0 µF or OL (overload/short)
A shorted capacitor shows 0 µF or an OL symbol on a capacitance meter because the internal dielectric has broken down completely.
In residential AC electrical schematics, a dashed line between two components typically indicates:
Answer: A mechanical linkage or shared enclosure
Dashed lines in schematics represent mechanical connections or components physically housed together, not electrical conductors.