Thermometer Trick for Vents

https://kylernyjy600.oakmontscope.com/posts/water-heater-repair-and-ac-repair-under-one-call-in-north-fort-worth-through-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