Very was 109 here today. I have a Carrier 16 seer 4 ton infinity heat pump. My home is a 2000 sq ft home with high celings. Set thermostat at 77, and it held there until 3:00p.m.. Then it went to 80 and has not come down yet. I have my unit serviced twice a year and just had it done. Measured the temp out of the return and intake. There is a 18 degree difference at the moment. Since its close to 20, I assumed that its doing its job. So, to my question. If my temp difference is 20, why cant my unit keep up?