HVAC Training Video: Checking the Charge in R22 and R410A Systems

Key Concepts

• Understanding pressure readings on low side (blue gauge) and high side (red gauge) for R22 and R410A systems.
• Importance of letting system run for at least 10 minutes before checking charge, dependent on metering device (TXV or piston).
• Conversion of pressures to temperatures using a pressure-temperature (PT) chart is crucial for accurate charge assessment.

R22 System Pressure Ranges

• Low Side (Blue Gauge):
  • Normal range: 58 psi to 85 psi
  • Below 58 psi (e.g., 55 psi): Indoor coil may freeze.
• High Side (Red Gauge):
  • Range: 120 psi to 300 psi
  • Depends on outdoor temperature and heat load.

R410A System Pressure Ranges

• Low Side (Blue Gauge):
  • Normal range: 102 psi to 145 psi
  • Below 100 psi: Indoor coil freezing risk.
  • Example: 102 psi ≈ 32.5°F, 97 psi ≈ 30°F (water in air can freeze on coil).
• High Side (Red Gauge):
  • Range: 200 psi to 480 psi
  • Requires PT chart for accurate charge calculation.

Metering Devices and Their Impact

• Piston:
  • Relies on pressure on low side gauge and temperature on vapor line.
  • Uses total superheat method.
• Thermostatic Expansion Valve (TXV):
  • Relies on high side gauge and temperature on liquid line.
  • Uses subcooling method.

Example Calculation

• Scenario with R410A and TXV:
  • High side pressure: 318.5 psi
  • Convert to saturated temperature (e.g., 100°F)
  • Measure temperature on liquid line (e.g., 90°F)
  • Calculate subcooling: 100°F - 90°F = 10°F
  • Compare actual subcooling to manufacturer’s target (e.g., 10°F is accurately charged).

Undercharge and Overcharge Scenarios

• Undercharge:
  • Example: Liquid line temperature = 96°F
  • 100°F - 96°F = 4°F subcooling (undercharged, needs more refrigerant).
• Overcharge:
  • Example: Liquid line temperature = 82°F
  • 100°F - 82°F = 18°F subcooling (overcharged, requires refrigerant removal).

Important Considerations

• Always check air flow before checking refrigerant charge.
• Incorrect assumptions about pressure settings can lead to inefficient operation or damage.

Additional Resources

• Free articles, books, and more information available at acservicetech.com.
• Topics covered include subcooling method, total superheat method, operating pressures, and troubleshooting.

Conclusion

• Properly identifying pressure and temperature relationships is critical for maintaining HVAC system efficiency and avoiding damage.