Have posted questions in the past and have gotten great I'm coming back to the well

I live in northern NJ, in a house that is about 2000 sq ft. and built in the 50's...lots of original windows with external storms.

We had a system installed a few months ago, in a house that did not have central air in the past. Trane xl16i 4 ton, with 2 zones, (up & down)...

the system imo just doesn't work right.. When it was 85 and humid, after 2.5 hours the house was still 78 degrees even though it was set to 70. When the sun is out and sunny, i can't get the system to 70..

It seems like the comperessor is always going. the contractor has been here twice already, first time they said they needed to add more coolant because the run from the compressor to A/h was long...the second time they were on the phone with the factory and told me the second stage was not wired properly....I'm still not happy.... shouldn't a 4 ton system be able to get 1 floor really cold...even if the temp is in the 90's...since the 4 ton system is supposed to be suffficient for the entire house.

Any suggestions as to what I should be looking for and what ? to ask the installer?

thanks in advance