Old - Biscuit - agree with everything except what was said about measuring temps. The infrared thermometer works excellent. When you shoot the intake, the ambient air temperature there is almost exactly the same as the plastic around it. If you shoot into the outlet vent and the AC has been running for about an hour or more, the air temp and the inside of the vent (plastic/metal) is about the same temperature. I can regularly get a 20 degree difference when I do this. Plastics and metals change temperature and become the temperature of the ambient air they are in over time. That being said, it is hot in Louisiana and the AC generally runs constantly from about 9AM until dusk. If your AC is cycling and turning off frequently, then it doesn't work as well, since the AC outlet vent will not have fully cooled even if the AC is working. This same infrared thermometer is also very useful for checking tire temps and wheel temps. I wouldn't leave home without one.