Air conditioning is not as easy as most people think. There are many mechanical and mathematical equations for each and every situation/installation.
Lets start fresh. Your AC worked for the first 2 years, now it can't keep up with the demand. The pressures i have read also are off wich would tell me dirty coils. But, you have had several technicians there to look at it and (like were i work)not all technicians purge their guages of air before putting freon in. Therefore putting noncondensibles into the system. Wich would result in the pressures you said. If what i suggest does not completely solve the problem then the system must also be evacuated and recharged.
What i did not see suggested was if your fan is belt driven or direct drive.
If it has a belt replace it. It is easy and make sure it is tight(less than a quarter of an inch if you pushed on it). Also make sure your supply fan is clean. (A dirty fan cannot move much air as well as a loose belt).
Maybe it was undersized to begin with? I had a house that we installed the system at construction. We ran the Heat Load properly. System cooled and heated perfectly. Well two years later the family sold the house. The new owners moved in and called the next summer with a problem of not cooling on Hot days. We came out in the morning..all was well. That afternoon..called back..was not cooling down to set point. After walking threw the house we realized that the owners' son had enough computer equipment in his room to land the space shuttle, Commercial refrigerator, 5 TV's, and no blinds on the windows. These things had raised the load of the house at least 1/2 ton.
here is the deal
when you read this do a few things for us since all the techs you have had there dont want to take the time or give the info. go to the hard ware store and get two thomoneters. put one in the return and one in the supply. air sucking in is return and air blowing out is supply.
write down this readings after fifteen minutes. the go out side and you will se two copper lines going to the unit. one has black insulation on it. take the temp on both lines.
write then down after five minutes.
post your readings here so we can see what is going on maybe. we also need the temp inside the house and outside temp to. this is not something hard to do and will give some of the real experts something to go by. pressures alone dont tell much and all any of us are doing is guessing. give us the name and model # of you unit.
one thin i forgot is the fan on top of the unit take the temp of the air blowing out of it to.
if you dont want to take any temps then have you tech take them but give us every thing. so far you have no given us anything to go by and to guess at it makes us no better then the guys that have been there
Bad txv? Restriction in evap. coil found refrigerant oil one time that clogged cap tubes off of metering device connection, posssible slightly bad compressor valves or (if its a heat pump) reversing valve leaking slighlty?
my unit is a 3-ton 10 seer rheem unit. I do not know the model number but I know it was put in 2001. I will call the tech tomorrow and get those readings. It seems wher ever I go the air conditioning is bad. went to my father -in- laws over the weekend in south alabama and his is doing the same thing and then came home this weekend and my houseis still doing it even after the tech came over and cleaned the coils and all and my parents house is doing the same thing. I have seen several people post about computers giving off heat, what about big screen tvs? I just got one two years ago but it is around the corner about 30 feet away. surely it isnt give off that much heat to raise the temp 5 and 6 degrees above the setpoint.