I did do a search and no thread seemed to answer my problem. We have had a pretty bad heat wave this year in OK and have really been testing our AC in the house. Well about 2 weeks ago it started weakening its effectiveness (Its 110 outside but it keeps it approx 80 inside) so it is working just not as well as it should. I have replaced the filter, cleaned the outside unit, replaced the thermostat on the wall and nothing, still will not cool the house. Tonight it did something weird though, we had a brown out (all lights darkened and AC kicked off then back on) I immediately checked the fuses outside at the AC unit and on my fuse panel and none were tripped the outside unit was still running but now it is blowing ambient air through all the vents. After I cleaned the condenser out it still wasn't working so I had a repairman come out and he said that the Freon was good but it was still dirty and he cleaned it for $70, I really want to make sure this could be something I can't fix before I shell out that kind of money again. Thanks for any help. BTW the outside unit is a Trane but it is probably 15+ years old.

With all of the things that you have done and none seemed to help the problem there is a possibility that the unit was doing all that it could do in that kind of heat. But you said it was blowing out ambient air out of the vents, that would indicate that the unit is not working. Have you tried to look at the evaporater coil? They have a tendency to get dirty over the years.
With your AC on you need to check to see if your compresser is running. One way to do this is with an amp meter. You should get a reading somewhere around 15 to 20 amps, depending on the size of you unit.

Where would I test the amps at? Are there specific lines? Sorry for all the questions but AC is not my strong point in the house. Thanks

Where would I test the amps at? Are there specific lines? Sorry for all the questions but AC is not my strong point in the house. Thanksbest to take the reading at the compressor only.