Symbols and Wiring Diagrams: Schematic Wiring Diagrams

 Attic Exhaust Fan System:

  • Manual Operation:
    • Fan motor mounted on the attic side.
    • Manual switch installed in the power line allows turning the fan on/off.
    • Simple operation by closing the switch to provide power to the fan.
  • Temperature Control:
    • Addition of a temperature control switch (thermostat) in series with the manual switch.
    • Thermostat senses attic temperature, bimetal expands with rising temperature, closing contacts and turning the fan on.
    • Real-world example: Both manual switch and thermostat wired in series to the fan motor.

Schematic Diagrams (Ladder Diagrams):

  • Purpose:
    • Best for troubleshooting, commonly used by service technicians.
    • Show the normal sequence of operations, but not the component location.
  • Structure:
    • Represented with graphic symbols instead of actual pictures.
    • Ladder sides (L1 and L2) signify power lines.
    • Parallel circuits are represented by rungs of the ladder.
    • Loads and switches are wired in series to control circuits.

Window Air Conditioner Diagram:

  • Basic Components:
    • Two loads: compressor and fan motor (operates both condenser fan and evaporator fan).
    • Selector switch: Turns unit off, fan on, or cooling mode.
    • Thermostat: Controls cooling mode, closes contacts as temperature rises.
  • Operation:
    • Fan can run for ventilation or switch to cooling mode.
    • Compressor operates only when the thermostat closes its contacts.

Advanced Window Air Conditioner Diagram with Relays:

  • Addition of Relays:
    • Controls relay coils rather than directly controlling the compressor or fan.
    • Relay coil controls the position of the switches (e.g., contactor for the compressor, fan relay for the fan).
  • Fan Switch Operation:
    • Fan On Position:
      • Power available to evaporator fan relay continuously.
      • Coil closes switch contacts, powering the evaporator fan.
    • Fan Auto Position:
      • Evaporator fan runs only when there is a call for cooling.
      • Thermostat calls for cooling, closing contacts between R and Y.
      • Power reaches contactor and evaporator fan relay, turning on compressor, condenser fan, and evaporator fan.

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Mechanics Introduction

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