I moved into a new home in Arizona in Nov 2015. The a/c worked fine until the
outside temperature got over 100 degrees. When it does, my thermostat will
stop at 78 degrees and can't be changed for up to 6 hrs. This summer we had
days of 112+. On those days thermostat would stay at 80 degrees. We like the
temp at 76-77 degrees, but can't do that when it is hot! Isn't that the point
of an a/c especially in Arizona?
Our a/c company has worked on the system for 3 months and still same problem,
but weather is getting cooler and soon it will be hard to tell if it is fixed
or not. Our house is 3360 sq ft and has 2 a/c units. The unit on the 1760 sq
ft side is a 3-1/2 ton a/c with 2 thermostats. That side of the house (East
side) stays as cool as we want it, even on very hot days. The 1600 sq ft side
of the house has a 2-1/2 ton a/c and it is the one with the problem. The a/c
company has replaced the condenser outside and the unit in the attic, but
yesterday it was 106 and still the same problem. I have asked if that unit
should be a 3 ton and they say no. What is the problem?

--
for full context, visit http://www.homeownershub.com/mainten...me-901871-.htm