I purchased a home in late May. Home is ~3,000 sq ft with 2,400 down stairs and 500 upstairs. Upstairs unit is a 1 1/2 ton with a 2 ton furnace.

Inspection was down in early April and nothing suggested to the A/C units just service them and hang some lines in the attic. After purchasing we had the HVAC company that did the inspection come out and service both units and hang the lines they suggested. The upstairs unit is now not keeping up in the heat of the day. I understand it should strain or be tough to keep at 100° heat but it should be getting to 80-82°.

HVAC company came and added less than a lb of Freon to the unit and blew out the coils and it still won’t keep up. The “spread” is 15-16° with outflow of ~60° and inflow into the return air of about 75-76°. My understand is that 18-20° is optimal??

Other issue is the thermostat doesn’t seem to recording temps correctly? What could be causing this? I understand this is a cheap thermometer but on one of the visits by the HVAC company his gauge read 76.1 and thermostats was reading 79°. What can cause this? Is just replacing thermostat sufficient?