Airflow
Cooling Delta-T and Split Temperature Sanity Check
A quick field reference for using return-to-supply temperature difference without over-reading one number.
How to use the number correctly
- Take return and supply readings as close to the equipment as practical, not at the farthest register.
- Let the system stabilize before trusting the number, especially after recent door openings or thermostat changes.
- Use wet conditions and airflow context; delta-T alone is not a charging method.
Quick interpretation
| Observed split | What it can mean | First checks |
|---|---|---|
| Below normal | High latent load, low charge, bypass, or weak compressor | Airflow, filter, blower speed, charge method |
| In normal band | System may be fine | Confirm airflow and customer comfort complaint |
| Above normal | Low airflow or restriction | Filter, coil, blower wheel, supply/return pressures |
Do not miss these traps
- A perfect split with terrible airflow can still leave rooms uncomfortable.
- A low split during pull-down after a hot start may be normal for the moment.
- Furnace temperature rise belongs to the nameplate range, not to cooling split rules.