Thermometer Trick for Vents

https://fernandokncz158.rivetgarden.com/posts/outdoor-ac-fan-not-spinning-in-north-fort-worth-is-a-repair-job-for-comfort-experts

Thermometer Trick for Vents Quick tip from our house: put a cheap kitchen thermometer in a supply vent after the AC runs 15 minutes, then check the air at the return. We see about an 18 degree drop when things are healthy