Problem: HVAC cooling blowing but not cooling.
I have a York Diamond 90 heating/ac unit for the top two floors of our town home (matched unit for bottom two floors, which works fine). The unit is 11 years old and has been serviced before each heating and cooling season.
About 4-5 years ago we experienced the cooling on the unit would not start up, but the fan would run. Typically the indoor unit would freeze up. The first thing the technician did was add freon. Later the company had us replace the outside compressor. Then a year or so later the problem started again, almost always thetedhnician added freon and it worked, for months. Every summer when really hot outside the same problem would occur, they would add freon and it would again for awhile.
Only think that works, for awhile: if I turn off the switch to blower, the blower shuts off. I let sit for a few minute. Then turn back on and the unit resets and starts to blow cool air ... For about an hour or so ... Then cooling stops and just blows hot air -- until I flip switch again, which I assume resets something.
What we've tried in last month:
1. Had outdoor compressor cleaned -- dramatically improved the strength of the air blowing from the fan
2. Had more freon added -- tested line temp at outdoor unit is something like 56 degrees
3. Change thermostat -- no help
4. Replaced circuit board -- helped for while
5. Wrapped the TXV valve -- no help.
6. Replaced air filter -- no change
What do we need to try next to solve the problem?
Thanks in advance for the help.