I have done a ton of research and am more confused now than when I started. I have a two story house built in 1967 in Corpus Christi, Tx with a 600 SF upstairs and 1200 SF down stairs. The house has not cooled well since I got it a year and a half ago. Last summer I just closed off all the vents and doors upstairs and did not go up there and the downstairs was ok. This last winter my sister-in-law moved in upstairs and I need to fix the AC to be able to cool both spaces adequately. The system I have now consists of a 14 year old Carrier evp coil (CD5BXA036000AAAA) and gas furnace (58PAV070-12) and an 18 month old Payne compressor (PA13NR036-C), the previous owner replaced the compressor when we bought the house. I have had 5 companies out to inspect the system and give quotes. They have ranged from replacing the old evp coil downstairs and adding a 2nd 1.5 ton 13 SEER unit upstairs $,$$$, to replacing the whole down stairs unit with a Carrier Infinity 21 SEER 5 ton unit with zone damper system, BIG $$,$$$. None of the companies have offered to do a manual J on the house and when I asked one of them about it they said that they only do it for big jobs or commercial use and proceeded to tell me that I needed a 5 ton unit because it was 1 ton per 400 sf. All I really want is for the whole house to be comfortable and to control the humidity in the house. I am not sure what my best option is at this point. Should I just patch up the system I have now and add a second unit upstairs or should I go with a larger unit with a variable speed fan and two stage compressor? Finance is a big concern but on the other hand I do not want to spend money over and over again to keep the system working. Any help would be appreciated.