Thanks for all of the replies. In answer to some of the questions:
The system has been on for a couple of months. The system consists of 3
units (one downstairs and 2 up). The upstairs is the problem. The home is
well insulated. I have actually paid 60% of the contract cost. The
contractor has a little more work to do (load balance and a couple of other
minor cosmetic things and agrees no additional payment is due until all of
the work has been completed. He has been very slow completing the final
items.)

The exterior temp I gave and the interior temp indicated by the thermostat
are correct.

To me as home owner, I don't care about all the technical aspects. My
question is simply: "I hired a company to design and install a system.
They did. Is it normally considered acceptable for the interior temp to to
be 81 when the exterior temp is 100 on a very sunny day."

If the answer is "Yes, any lower and your system would be oversized" then
fine. If the answer is "No" then the contractor should correct the
situation be it the freon charge level, unit size, duct design, airflow
rate, j page calculations, or whatever.

I just had a new HVAC system installed in a new house and have not paid for
it yet.

If you have not paid, you must return your 81 degree air and get
hotter air in return. I'm sure they have an air exchange place
nearby.

Your cool air will be sold to defray your debt.


Today the temperature is 100 outside. I have my thermostat set to
77 and the actual temperature is 81. (This is upstairs, downstairs a
separate system is maintaining the selected temperature.)

I am getting about a 20 degree drop. Is that acceptable or should the
system be doing better?