Thermometer Trick for Vents

https://blogfreely.net/galimelfxx/comfort-experts-on-refrigerant-leaks-and-ac-repair-for-north-fort-worth-systems

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