It's been over 100 for several weeks here in Texas and I get the part that my 2500 sq ft single story house won't be a cool 72 degrees. However, in the last week it has stopped functioning the way it has for the previous 9 summers. Up to 84 or 85 degrees inside, with the unit set at 75 during the day. I can't deal with the Texas heat anymore! The repair guy came out two times and I feel like I am getting ripped off. Need help!
1 week ago: he said the filter needed cleaning, washed it and said he added freon. Temp dropped at 1 degree per hour. Very slow. The following days were marginally better.
Today: said he'd left in a hurry and should have added freon. Put in 2 lbs. but charged me nothing. He gave me a bunch of numbers I wrote down but they mean nothing. ( I am educated... just not about air conditioners!) the temp stayed low for the early part of the day, but once it started baking outside up it went. Currently 84 again. The unit outside shuts off and then goes back on, with it set at 75. Should it be turning off and then back on? Any clues as to what the problem is? They are now telling me I'll be charged if they come out and "nothing is wrong" with the unit.
I am not an a/c hypochondriac and am hoping for some honest help and appreciate any that you can provide.

That's not surprising for over 100! Getting a house to 75 when the temp is almost 30 degrees higher outside is impossible.

I think they are right... Most likely there is nothing wrong with your AC, it is just straining in the extreme heat. When it got to 114 in California, my dad's house wouldn't go below 84. Especially if the sun is on the house, that will warm it up.

Make very sure that you have heavy drapes or blinds closed over the windows all day long, to keep the sun out. Sunlight coming in windows is the major cause of heat gain inside a house during the summer. Note that plastic mini-blinds will not work adequately. Heavy cloth drapes that are lined with white tend to be best.

If I ask you how often you clean or change your filter you are going to tell me every two or three months. Well I won't doubt you but having a dirty filter is the biggest cause of complaints that I have. And even a bigger problem is having a dirty coil caused by not changing the filter often enough. To clean a coil is quite a job, to do it right a person has to take it out and steam clean it, but it can be done, not as good but well enough to tell a difference by taking off the front of the coil box, and if you are lucky and have a slab coil the bottom of the coil will be exposed, if you have an A coil then you will have to remove another piece of metal to expose th bottom of the coil. When you can see the coil you can see if it is very dirty use a brush to clean the coil brushing the sam direction that the fins run. You need to spread a newspaper over the top of the heat exchanger to not let the trash fall into the furnace. But do not forget to take out the paper when finished. It is very possible that if your coil is dirty and you clean it you may then have to add more freon because the reading on the gauges will change.