HVAC Exam Review Flashcards

Motor Driving Devices

  • There are two basic types of motor driving devices.

Testing Electric Motors

  • When working on an electric motor, it's important to test the windings to ensure they're in good condition.
  • A megger is a piece of test equipment used for this purpose.
  • Alternatively, an ohmmeter can also be used.

Contactor Replacement

  • Major reasons for replacing a contactor:
    • A bad winding (the coil for the magnetical winding that holds the contacts).
    • Contacts that are burnt out or have debris stuck in them.
    • The mechanical linkage is faulty (e.g., issues with the spring).

Coil States

  • Three states of a coil:
    • Open: The coil becomes an open line due to breaking.
    • Shorted: The coil is shorted.

Motor Protection

  • Simplest form of motor protection used in the field: Fuse

Cadmium Sulfide Cell (Cad Cell)

  • Function: Detects light in a furnace.
  • Location: Found inside furnaces (gas-fired or oil-fired).
  • Operation: Adjusts resistance based on the changes in the volume of light it detects.
  • Application: Used in oil-fired furnaces because flame rods and thermal couples are used for flame detection in natural gas furnaces.
  • Cad cells are used because of spark electrodes sparking and atomizing the oil at the nozzle to lighten it up.
  • The system drops on the system light. So it goes from, like, 20002000 to 900900.
  • Voltage: 2424 volts.

Electric Heating Systems

  • Variable speed fan is used.
  • Sequencing is used in electric heating systems to stage the electric heat.
  • The reason is to prevent the entire system from turning on at once, which would draw too many amps and trip the breaker, and prevent overshooting of power.
  • Example: If emergency heat is turned on, there might be 30 kW, which is then sequenced in stages.

Boilers

  • Two mediums used to heat a house in a boiler: Steam or hot water.

Cooling System

  • Understanding the different questions comes down to the type of system:
    • Electric load
    • Mechanical functioning

Contactor vs. Relay

  • Difference between a contactor and a relay:
    • Contactors are generally used for higher voltage and amperage (over 2020 amps),
    • Relays are used for lower voltage and amperage (less than 2020 amps).
    • Contactors are used for heavy-duty loads,
    • Relays are used for lighter loads.
    • The contacts on a contactor are physically visible, whereas you have to open a relay to see the contacts.

Overload Checks

  • Easiest type of overload to check:
    • Visually: Circuit breaker (to see if it's popped).
    • Physically: Fuse (check with multimeter).

Contactor Parts

  • Two parts of a contactor: Contacts and mechanical linkage.

Thermostats

  • Two types of thermostats:
    • Line voltage
    • Low voltage
    • Communicating
    • Wi-Fi
    • Bimetal

Transformers

  • Function: Used to step up or step down voltage.

Control Systems

  • Type of control system used on most residential air conditioning systems:

Thermostats and Connections

  • When the room gets hot, the connection is made, and when it gets colder, the connection breaks.
  • Considerations:
    • Full temperature for cooling.
    • Snapback.
    • 24 volts.
    • Arcing which is bad.

Pressure Switch

  • A pressure switch is a device that opens or closes a set of contacts when a certain pressure is applied to the diaphragm and the switch.

Industry Standard Colors

  • Power: Red.
  • Fans: Yellow.
  • Cooling: Green or Blue.
  • Red, green, yellow, white.

Types of Loads

  • Two types of loads:
    • Inductive.
    • Resistive.
    • Compressor.

Shaded Pole

  • Torque.

Capacitors

  • Rating used for capacitors: Microfarads (UF).

Oil-Fired System

  • In an oil-fired system, an oil filter is in line with the oil, before the oil reaches the oil pump burner.

Thermostat Voltage

  • Control voltage: 24 volts.
  • Residential: 24 Volts.

Electrical Systems

  • The control voltage: 24 volts
  • Hot legs: 2

Venting

  • Electric furniture is not powered with flue vent from heat exchanger.

Hot Surface Ignitors

  • Most hot surface ignition devices are made of silicon sulfide (SiS).

Bearings

  • Two types of bearings used in the HVAC industry: Ball bearing and sleeve bearing.

Heat Pump Thermostat

  • What is the o terminal on a heat pump thermostat control?

Shorted Wires

  • The coil of a contactor is reading zero ohms: shorted state.