CSLB C-20 HVAC ContractorCooling and RefrigerationEasy
A technician measures return air entering the evaporator coil at 75°F and supply air leaving the coil at 55°F on a properly operating split system. What does this 20°F temperature split indicate?
- AThe evaporator coil is frozen due to overcharge
- BThe system is undercharged with restricted airflow
- CThe system is operating normally within the typical delta T range
- DThe compressor is not pumping efficiently
Show answer & explanationAnswer & explanation
Correct answer: C. The system is operating normally within the typical delta T range
A properly functioning residential AC system typically produces a temperature drop of 16–22°F across the evaporator coil under normal indoor conditions. A 20°F split falls within this normal range, indicating correct airflow and charge.
Why the other options are wrong
- A. A frozen coil typically results from low airflow or undercharge, not indicated by a normal split.
- B. Undercharge or restricted airflow usually produces a split higher than 22°F, not a normal reading.
- D. A weak compressor would produce a smaller, not normal, temperature split.
Evaporator Delta T
The temperature drop between return air and supply air across the evaporator coil, used as a quick diagnostic indicator of system performance.
- Normal split range is about 16–22°F
- Depends on indoor humidity and airflow (CFM per ton)
- Abnormal splits point to airflow, charge, or coil problems
Memory trick: Twenty degrees means 'twenty-twenty' airflow vision — system's fine!