A/C not holding at temperature. I have a RITETEMP GPMG8085CS thermostat. I have had the A/C guy out here twice. The original issue was a bad capacitor in the unit which was replaced (he also cleaned the condenser coil). After noticing the temp not going cooler than 69.5 I called him back out. He checked the freon and said it's fine but that he could add a pound or two. So he added 1.5 lbs. It still wasn't cooling correctly and doing the same thing. Then last week (after me playing with the settings, tightening wires, resetting the thermostat 3 times, changing the batteries in the t-stat etc, it started working fine. Now again today it's back to it's old self. Any advice?

Yes get yourself a different A/c guy

I meant that it's still not working right. Also the filter is new, the outside line is cold to the touch etc. The unit is 15 yrs old...