How to calculate approach temperature
Approach = liquid line temperature − outdoor air temperature
Measure outdoor air temperature where air enters the condenser coil, in the shade. Measure liquid line temperature near the liquid service valve.
Worked example
The liquid line is 105°F and outdoor air entering the coil is 90°F. Approach is 105 − 90 = 15°F, which is in range (10–20°F).
What a high approach means
A high approach means the condenser isn't shedding heat well. Check for a dirty condenser coil, a weak condenser fan, hot air recirculating, or overcharge.
High-efficiency condensers with large coils often run a lower approach. Compare against the manufacturer's data when you have it.
Questions
What is a normal condenser approach temperature?
Air-cooled condensers usually run a 10–20°F approach. High-efficiency units can run lower.