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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