Diagnosing A/C Systems : Temperature Split and Evaporator TD

 Understanding SEER Ratings and System Performance:

• 10 SEER Unit:

  • Condenser Split: 30° ± 5°
  • Example: 95°F ambient air, 125°F condensing temperature, resulting in a 30° split.
  • Subcooling: 10°F (125°F condensing temperature - 115°F liquid line temperature).
  • Evaporator Temperature Difference (TD): 35°F (75°F return air - 40°F evaporator temperature).
  • Superheat: 10°F (50°F suction line temperature - 40°F evaporator temperature).

• 12 SEER Unit:

  • Condenser Split: Decreases with higher SEER.
  • Example: 95°F ambient air, 120°F condensing temperature, 30°F split.
  • Subcooling: Remains at 10°F (120°F condensing temperature - 110°F liquid line temperature).
  • Evaporator TD: 35°F, with consistent superheat due to the thermostatic expansion valve.

• 13 SEER Unit (New Minimum):

  • Condenser Split: 20° (95°F ambient air, 115°F condensing temperature).
  • Subcooling: 10°F, consistent with previous units.

• 14 SEER Unit:

  • Condenser Split: 15° (95°F ambient air, 110°F condensing temperature).
  • Subcooling: Remains at 10°F, but high side pressure and power consumption are reduced.

General Troubleshooting Procedures:

1. Ensure Proper Airflow:

   • Check the filter; clean if necessary.
   • Average airflow should be about 400 CFM per ton of capacity.

2. Determine Normal Operating Conditions:

   • Establish normal evaporator temperature, superheat, condensing temperature, and subcooling.

3. Assess System Conditions:

   • Evaluate if each condition is normal, higher than normal, or lower than normal.

Evaporator Temperature Difference (TD) Analysis:

• Normal Evaporator TD: 30° to 40° below return air temperature.

  • Example: 75°F return air results in 35°F to 45°F evaporator temperature.

• High Evaporator Temperature:

  • Indicates high pressure, possibly due to a flooded evaporator or excessive heat load.

• Low Evaporator Temperature:

  • Indicates starving of refrigerant or low heat load.

• Effect of Evaporator TD on Temperature:

  • Higher evaporator temperature: TD below 30°F.
  • Lower evaporator temperature: TD above 40°F.
  • Keep evaporating temperature above freezing (32°F) to avoid issues since air conditioning systems lack automatic defrost mechanisms.