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Electrical Controls and Safety Flashcards

6 cards from real HVAC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 6 Electrical Controls and Safety flashcards as text

  1. What voltage is typically used for the low-voltage control circuit in a residential HVAC system?

    Answer: 24V AC

    Residential HVAC control circuits operate at 24V AC, supplied by a step-down transformer from the 120V or 240V power supply.

  2. What is the function of a contactor in an air conditioning system?

    Answer: To switch high-voltage power to the compressor and condenser fan motor

    A contactor is an electrically operated switch that uses a low-voltage coil to close contacts that supply high-voltage power to the compressor and condenser fan.

  3. What does a capacitor do in an HVAC motor circuit?

    Answer: Stores electrical energy to help start and run single-phase motors

    Capacitors store electrical energy and create a phase shift that provides starting torque and improves running efficiency in single-phase HVAC motors.

  4. What is the purpose of a disconnect switch near an outdoor HVAC unit?

    Answer: To provide a local means of de-energizing the unit for safe service work

    The disconnect switch allows service technicians to safely de-energize the outdoor unit locally without going to the main electrical panel, as required by OSHA and NEC.

  5. What does a high-pressure switch in a refrigeration system do?

    Answer: Shuts down the compressor if refrigerant pressure exceeds a safe limit

    The high-pressure switch is a safety device that opens and shuts off the compressor if discharge pressure rises above a safe setpoint, preventing equipment damage.

  6. What is the purpose of a time-delay relay (TDR) in an HVAC control circuit?

    Answer: To introduce a time delay in circuit operation, such as preventing immediate compressor restart

    Time-delay relays prevent compressor short cycling by requiring a minimum off time before restarting, protecting the compressor from liquid slugging.