Thermometer Trick for Vents

https://andrerdzu732.birchreport.com/posts/storm-and-power-outage-advice-from-comfort-experts-for-ac-repair-in-north-fort-worth-neighborhoods

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