Diagnosing A/C Systems : Dirty Condenser

 Overview:

• A dirty condenser coil can significantly impact the performance of an air conditioning system, leading to higher condensing temperatures and potential inefficiencies. The effects can differ based on whether the system uses a fixed bore metering device or a thermostatic expansion valve (TEV).

Effects of a Dirty Condenser Coil in Systems with a Fixed Bore Metering Device:

1. Condensing Temperature:

   • Condition: Increases above normal.
   • Reason: The dirty condenser restricts heat rejection, causing the condensing pressure and temperature to rise.

2. Subcooling:

   • Condition: Remains relatively normal, with a possible slight increase.
   • Reason: The amount of refrigerant remains unchanged, so subcooling is not significantly affected.

3. Evaporator Temperature:

   • Condition: Increases.
   • Reason: The higher condensing pressure forces more refrigerant into the evaporator, raising the evaporating temperature.

4. Superheat:

   • Condition: Decreases, possibly to zero.
   • Reason: The increased refrigerant flow into the evaporator results in less heat absorption, leading to lower or no superheat, which may cause liquid floodback to the compressor.

Example: Dirty Condenser on a 10-SEER Air Conditioning System with R22 (Fixed Bore Metering Device):

• 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.

• Dirty Condenser Conditions:

  • High side pressure increases to 360 PSIG → 145°F condensing temperature.
  • Condenser split increases to 50°F (145°F condensing temperature - 95°F ambient air).
  • Subcooling: Slight increase to 15°F, still relatively normal.
  • Low side pressure increases to 102 PSIG → 60°F evaporating temperature.
  • Evaporator temperature difference (TD) decreases to 20°F (80°F return air - 60°F evaporator temperature).
  • Superheat drops to 0°F, indicating liquid refrigerant entering the suction line, which risks damaging the compressor.

Effects of a Dirty Condenser Coil in Systems with a Thermostatic Expansion Valve (TEV):

1. Condensing Temperature:

   • Condition: Increases above normal.
   • Reason: The dirty condenser restricts heat rejection, causing the condensing pressure and temperature to rise.

2. Subcooling:

   • Condition: Remains relatively normal, with a possible slight increase.
   • Reason: Although there is more refrigerant available for subcooling, the TEV regulates refrigerant flow effectively.

3. Evaporator Temperature:

   • Condition: Remains normal.
   • Reason: The TEV adjusts refrigerant flow to maintain the correct evaporating temperature.

4. Superheat:

   • Condition: Remains normal.
   • Reason: The TEV is designed to maintain consistent superheat regardless of changes in the system's high side pressure.

Example: Dirty Condenser on a 10-SEER Air Conditioning System with R22 (TEV System):

• 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.

• Dirty Condenser Conditions:

  • High side pressure increases to 360 PSIG → 145°F condensing temperature.
  • Condenser split increases to 50°F.
  • Subcooling: Slight increase to 15°F, still relatively normal.
  • Low side pressure increases slightly to 76 PSIG → 45°F evaporating temperature.
  • Evaporator TD remains normal at 35°F (80°F return air - 45°F evaporator temperature).
  • Superheat remains normal at 10°F (55°F suction line temperature - 45°F evaporating temperature).

Key Takeaways:

• High Condensing Temperature: A primary indicator of a dirty condenser coil, leading to higher system pressures and inefficiency.
• Fixed Bore Metering Device: A dirty condenser can cause higher evaporator temperatures, lower superheat, and potential compressor damage.
• TEV Systems: Although the evaporator side may operate normally, the increased high side pressure still results in higher compressor amp draw and reduced system efficiency.