Thermometer Trick for Vents
https://shanefadk435.inkharbory.com/posts/ac-repair-for-heritage-homes-by-comfort-experts-in-north-fort-worth-4
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