Thermometer Trick for Vents

https://damienpuen618.currentvale.com/posts/compressor-problems-and-ac-repair-choices-for-north-fort-worth-homeowners-at-comfort-experts-2

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