72 Degrees A/C & Heating

I recently purchased a home that has a 16 seer Goodman split system gas horizontal that was installed in May 20012. Immediately after moving in, I noticed that the a/c did not cool the home to my desired temperature of 75 degrees. When I went into the attic to see what the problem may be, I noticed that the plenum was half the size of the unit and was that makes it really inefficient. I called 72 Degrees and they sent someone to verify what I was saying. The person they sent out agreed that the plenum was way too small and they replaced it. When they were done, I tried the a/c out for another week to see if it helped with the cooling of the home, but still, my unit will not drop below 78 degrees and if I have it set at 78 degrees it won't shut off. So, I called them to say that when the thermostat is set at 79, it will work properly, but when you try to drop the temperature, it will consistently run. They sent the same guy out to check the system and he determined that the system was running great with a 23 degree split. My complain was not the temperature split, it is that the system won't go below 79 without consistently running all day, which totally defeats the purpose of a 16 seer system because my bills keep getting more and more expensive. My thoughts are that if the system is running as great as they say it is, then it is obviously undersized and would require a supervisor to go out and determine if this is true.

I then tried to call them about retrieving paperwork from the original sale so that I can verify that a proper Manual J Heat Load was taken to verify what size system was meant for the home and also to get supervisor to call me about the issues that i'm experiencing. I was told that this paperwork would have to be pulled and that i'd receive a call as soon as it is done. I waited 4 days until I called back and when I did, the woman on the phone said that she'd pull the paperwork right then and email it to me. I have yet to receive that email and that was two days ago. I called today and asked to speak with someone that deals with installations and installation paperwork and I was sent to voicemail.