Symbols and Wiring Diagrams: Diagram Standards

 Introduction:

  • No official rules but switch designations and labeling are fairly standard.
  • Operating controls (thermostats, vandals, etc.) are typically shown in the open position.
  • Safety controls (high pressure, low pressure switches, limit switches, overloads) are shown in the normally closed position, only opening during malfunctions.

Review of Relay Contacts:

  • Relay contacts are shown with the relay coil de-energized.
  • Normally closed (NC) contacts open when the coil energizes.
  • Normally open (NO) contacts close when the coil energizes.

Typical Schematic Diagram (Air Conditioning Unit with Gas Heating):

  • Operating Controls: Fan switch, cooling thermostat, heating thermostat are shown in open position.
  • Safety Controls: Limit switch, low pressure switch shown in normally closed position.
  • Relay Contacts: Indoor fan relay coil shown de-energized with normal contact positions (NO to high speed, NC to fan switch).

Detailed Schematic Diagrams:

  • Numbered lines on the left side identify circuits.
  • Numbers on the right side indicate affected circuits on the left and contact configuration (normally closed).
  • Example: Line 1 has compressor and condenser fan; Line 3 has high speed indoor fan motor; Line 4 has low speed indoor fan motor.
  • Detailed schematics are less common but useful for troubleshooting.

Reading Wiring Diagrams:

  • Use diagrams like a map to determine power sources, switch controls, load controls, and normal sequence of operations.
  • Example (Continuous Fan Operation):
    • Fan switch to ON position energizes indoor fan relay coil (Line 7), closing contacts on Line 3 (high speed blower) and opening contacts on Line 4 (low speed blower).

Operation Modes:

  • Cooling Mode (Fan Auto Position):
    • Cooling thermostat closes, energizing AC contactor coil and indoor fan relay coil.
    • Compressor and condenser fan start, indoor fan runs in high speed.
  • Heating Mode (Fan Auto Position):
    • Heating thermostat closes, energizing gas valve.
    • Gas flows to burners, ignites, and heats exchanger.
    • Fan switch closes, running blower in low speed.

Typical Wiring Diagram Layout:

  • Includes schematic diagram, pictorial diagram, component codes, legend, wiring information, wire color codes, and description.
  • Example: Air conditioning condensing unit with detailed electrical components and wiring.

High Voltage Diagram:

  • Line voltage wires enter contactor (L1, L2).
  • Components: Dual run capacitor, contactor, compressor terminal box.

Low Voltage Diagram:

  • Components: Contactor coil, low pressure control.
  • Low voltage from thermostat (yellow wire) passes through low pressure control to contactor coil.
  • Example: Fixed low pressure control in the control box.

Summary:

  • Schematic diagrams (ladder diagrams) are essential for troubleshooting.
  • Diagrams represent elements with graphic symbols.
  • Standards for showing controls and safety devices help in understanding and troubleshooting systems.

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