Thermometer Trick for Vents

https://shanefadk435.inkharbory.com/posts/comfort-experts-new-ac-installation-for-north-fort-worth-homes-past-the-repair-stage

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