HVAC Diagnostic Chart (Fixed Metering vs. TXV System)

This chart provides troubleshooting data for air conditioning system diagnostics, comparing Fixed Metering and TXV (Thermal Expansion Valve) Systems. It outlines how different fault conditions impact key system parameters, including:

• Suction Pressure (Low Side)
• Head Pressure (High Side)
• Superheat
• Subcooling
• Compressor Amps
• ΔT (Temperature Differential)

Fixed Metering System Diagnostics:

• Low Charge: ⬇ Suction & Head Pressure, ⬆ Superheat, ⬇ Subcool & Amps
• Overcharge: ⬆ Suction & Head Pressure, ⬇ Superheat, ⬆ Subcool & Amps
• Low Airflow: ⬇ Suction Pressure, ⬆ Head Pressure, ⬇ Superheat, Norm Subcool & Amps
• Dirty Condenser: ⬆ Head Pressure, ⬆ Compressor Amps, ⬇ ΔT
• Liquid Line Restriction: ⬇ Suction & Head Pressure, ⬆ Superheat, Norm Subcool
• Oversized Piston: ⬆ Suction Pressure, ⬇ Superheat, ⬇ Subcool
• High Return Air Temp: ⬆ Suction & Head Pressure, ⬆ Compressor Amps

TXV System Diagnostics:

• Liquid Line Restriction: ⬇ Suction Pressure, ⬆ Superheat, Norm Subcool
• Overfeed / Loose Bulb Insulation: ⬆ Suction Pressure, ⬇ Superheat, ⬇ Subcool
• Slight Low Charge: Norm Suction & Head Pressure, ⬆ Superheat, ⬇ Subcool
• Slight Overcharge: Norm Suction & Head Pressure, ⬇ Superheat, ⬆ Subcool
• Low Airflow: ⬇ Suction Pressure, Norm Head Pressure, ⬇ Superheat, ⬆ Subcool