Diagnosing A/C Systems : TEV Flooding

 Overview:

• TEV flooding occurs when too much refrigerant enters the evaporator, causing an imbalance in the system. This can lead to issues like compressor floodback, where liquid refrigerant enters the compressor, potentially causing damage.

Key Indicators of TEV Flooding:

1. Evaporator Temperature:

   • Condition: Typically remains normal but may slightly increase.
   • Reason: The refrigerant is still absorbing heat in the evaporator, maintaining a relatively stable evaporator temperature.

2. Superheat:

   • Condition: Lower than normal or potentially zero.
   • Reason: The excess refrigerant in the evaporator is not fully vaporizing, leading to low or no superheat. This can result in liquid refrigerant returning to the compressor, a condition known as floodback.

3. Condensing Temperature:

   • Condition: Generally remains normal but may slightly decrease.
   • Reason: Although more refrigerant is entering the evaporator, the impact on the condensing temperature is minimal. Any decrease would be minor and dependent on the severity of the flooding.

4. Subcooling:

   • Condition: Remains normal.
   • Reason: The amount of refrigerant in the condenser remains adequate, so subcooling does not significantly change.

Example: TEV Flooding on a 10-SEER Air Conditioning System with R22:

• Normal Operating Conditions:

  • Low side pressure: 69 PSIG → 40°F evaporating temperature.
  • High side pressure: 278 PSIG → 125°F condensing temperature.
  • Ambient air: 95°F, resulting in a 30°F condenser split.
  • Subcooling: Approximately 10°F.
  • Superheat: Normal at around 10°F.

• TEV Flooding Conditions:

  • Evaporator Side:

    • Low side pressure may remain at 69 PSIG → 40°F evaporating temperature (could slightly increase depending on the severity of flooding).
    • Evaporator temperature difference (TD) remains normal at 35°F (75°F return air - 40°F evaporator temperature).
    • Superheat decreases to 0°F, indicating liquid refrigerant is leaving the evaporator and entering the suction line, leading to floodback and potential compressor damage.

  • Condensing Side:

    • High side pressure and condensing temperature remain relatively normal.
    • Condenser split remains normal at 30°F.
    • Subcooling remains normal at around 10°F.

Common Causes of TEV Flooding:

• Poor Installation: The TEV bulb may not be securely fastened to the suction line, leading to improper temperature sensing and control of refrigerant flow.
• Incorrect TEV Application: Using the wrong TEV for the specific system can cause it to malfunction and allow excess refrigerant into the evaporator.
• TEV Out of Adjustment: The TEV may need a superheat adjustment to ensure proper operation.

Key Considerations:

• Check Superheat: Superheat is a quick and easy indicator of TEV flooding. Regularly check it, especially after installations or repairs.
• System Performance Check: Perform a complete system performance check after installation or repair, and cycle the unit on and off a few times to verify proper operation.
• Return Air Temperature: Ensure return air temperature is within 5°F of design specifications. Low return air temperatures can contribute to TEV flooding.
• Start-Up or High Load Conditions: Normally, a TEV will starve the evaporator under these conditions, but if flooding occurs, it indicates a malfunction.

Preventive Measures:

• Proper TEV Installation: Ensure the TEV bulb is correctly positioned and securely fastened.
• Correct TEV Selection: Use the appropriate TEV for the system to avoid flooding issues.
• Superheat Adjustment: If flooding is detected, consider adjusting the TEV’s superheat setting to correct the issue.