1. Core Concept: Vapour Compression Refrigeration System (VCRS)
Both Window and Split ACs operate on the VCRS cycle.
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Refrigerants used: R-22 (older), R-32, R-410A (High pressure), R-290 (Propane – Flammable).
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The Four Main Stages:
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Compression: Low pressure, low temperature (LP/LT) vapour $\rightarrow$ High pressure, high temperature (HP/HT) vapour.
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Condensation: HP/HT vapour $\rightarrow$ HP/HT liquid (Heat rejected to outside).
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Expansion: HP/HT liquid $\rightarrow$ LP/LT liquid/vapour mix (Pressure drop).
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Evaporation: LP/LT liquid $\rightarrow$ LP/LT vapour (Heat absorbed from room).
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2. Window Air Conditioner (Unitary System)
A self-contained unit where all components are housed in a single chassis.
Technical Components
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Compressor: Usually Hermetically Sealed Reciprocating or Rotary type.
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Condenser: Air-cooled, finned-tube type (located at the rear/outside).
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Evaporator: Finned-tube type (located at the front/indoor side).
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Expansion Device: Capillary Tube (Fixed orifice).
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Fan Motor: Single motor with a Double-ended shaft. One end drives the Centrifugal Blower (Evaporator side), and the other drives the Propeller Fan (Condenser side).
Key Mechanic Facts
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Air Circuit: Uses a “Ventilation Damper” to bring in a small amount of fresh air.
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Slingshot Ring: The condenser fan has a ring that picks up condensate water from the base tray and splashes it onto the condenser coils to assist cooling (Sub-cooling).
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Mounting: Requires a wall opening or window frame; higher vibration/noise because the compressor is inside the room perimeter.
3. Split Air Conditioner
Separates the “noisy” components from the “cooling” components.
System Division
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Indoor Unit (IDU): Contains Evaporator coil, Filter, Cross-flow fan (Tangential fan), and Control PCB.
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Outdoor Unit (ODU): Contains Compressor, Condenser coil, Propeller fan, and Expansion device (Capillary or EEV).
Installation/Technical Specs
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Refrigerant Piping: Connected via “Suction Line” (larger diameter) and “Liquid/Discharge Line” (smaller diameter).
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Flare Nut Joints: Critical point for leak testing using soap solution or electronic leak detectors.
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Inverter Technology: Uses a Variable Frequency Drive (VFD) to change compressor speed. Unlike “On/Off” ACs, it doesn’t stop the compressor, saving 30-50% energy.
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4. Comparison for Competitive Exams
| Feature | Window AC | Split AC |
| Installation | Easier (single hole/window) | Complex (requires copper piping & vacuuming) |
| Noise Level | High (Compressor is nearby) | Low (Compressor is outdoors) |
| Expansion Device | Capillary Tube | Capillary or Electronic Expansion Valve (EEV) |
| Efficiency | Lower (limited coil size) | Higher (larger condenser area possible) |
| Maintenance | Easier (pull out the chassis) | Harder (requires gas charging if leaks occur) |
5. Important Exam Keywords & Troubleshooting
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Evacuation: Removing air and moisture using a vacuum pump before gas charging. Moisture causes Capillary Choking (ice formation inside the tube).
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Purging: Clearing air from hoses using a small amount of refrigerant.
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Superheating: Ensuring only vapour enters the compressor to prevent Liquid Slugging (which breaks valves).
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Short Cycling: AC turns on/off too rapidly. Causes: Oversized AC, dirty filters, or faulty thermostat.
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Frost on Evaporator: Usually caused by Low Refrigerant or Restricted Airflow (dirty filters).
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Pump Down: Moving all refrigerant into the Outdoor Unit (ODU) for repairs or shifting.
- Anemometer: Measures air velocity at the grill.
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Psychrometer: Measures Dry Bulb (DBT) and Wet Bulb (WBT) temperatures to check humidity.
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Halide Torch / Electronic Leak Detector: Used for finding gas leaks.
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Brazing: Joining copper tubes using Silver Solder and Oxy-Acetylene/LPG torch.
Pro-Tip for Exams: Always remember that in a Split AC, the Capillary Tube is almost always located in the Outdoor Unit to reduce noise of the refrigerant expansion inside the room.