Delta T (ΔT) cooling measures the temperature difference between return air and supply air to assess overall system cooling capacity and efficiency. A typical delta T ranges from 15-22°F for properly functioning systems. This measurement directly indicates how effectively the evaporator removes heat from the air and serves as a quick performance baseline.
Measurement and Standards
Technicians measure return air temperature (typically 70-80°F) and supply air temperature (typically 50-65°F) at the same locations for accurate readings. The difference between these values is delta T. A low delta T below 12°F suggests restricted airflow, low refrigerant, or reduced compressor capacity, while excessively high delta T above 25°F indicates oversizing or other airflow problems.
Diagnostic Value
Delta T provides quick system health assessment before performing detailed pressure and subcooling tests. Low delta T combined with high suction pressure indicates possible low airflow, dirty filters, or blocked ducts. This measurement helps technicians prioritize further diagnostics and verify proper operation after service completion.