Home AC Help

[CrazyEyez]

My home central AC doesn't seem to be working up to its potential. The air coming out of my vents is not much cooler than room temp. Therefore it runs a lot and takes a long time to cool the house down if it gets warm.

Are there basic troubleshooting techniques I can try before I pay to have someone come out and look at it? I've hosed off the unit outside. Inside, my filter does need to be replaced as it's filthy and about 6 months old. How likely is that to be the only problem? Anything else?