OK, I went out and took the access panel off my old system and found it's an HS16-651, so it's a 5 ton unit. Also, I went down and pulled the access panel on the furnace and checked things out more thoroughly and my furnace is NOT a variable speed furnace, even though the motor is a variable speed blower motor. It turns out the motor isn't original to the furnace. It's a 92% efficient lennox furnace and 11 years old. And to further clarify, my old system cools adequately on most days, but not on the hottest days when temps are at or above 100ºF here, which occurs on anywhere from 5 to 25 days a year here depending on the year. On other "normal" hot days it cools the house only adequately, but not efficiently or easily. It runs quite a bit to maintain an adequately cool house and the air coming out of the vents isn't all that cold feeling. I think part of this is a venting problem and we only have the minimum amount of return vents that we should have, but I've felt the other part is the A/C itself. That's when it runs all the time, but never gets the house below about 76ºF or so in the coolest part of the 1st floor and about 80ºF in the coolest part of the 2nd floor. Thanks again for all the help and replies.

A properly sized unit should be able to maintain reasonable humidity levels (though maybe not at 78 degrees without a dehumidification mode). The dual-stage unit will help control humidity. The only way of extra dehumidification with the XL16i that I know of is with the TCONT803/Honeywell TH8321 thermostat, which will overcool to control humidity. Ask your contractor why he proposed the VisionPRO IAQ when the BK terminal is already in use by the XL16i, thus not allowing the dehumidification feature of the VisionPRO IAQ (which is great as it actually slows down the blower). If you want an alternative that can make use of the VisionPRO IAQ, I'd go with the XL15i. It's a single-stage unit, but sized properly it should control humidity fine with the added advantage of the VisionPRO IAQ. Here are possible setups (ask your contractor what size he would recommend--I would NOT go with a 3 ton for your size home). Now, there are different air handlers that can go with these units, but the 4TEE3F39 air handler is tall due to the Vortica blower. The 4TWX5024A1000A (2-ton XL15i) with the 4TEE3F31B1000A yields 13.00 EER, 15.25 SEER and 8.60 HSPF. The 4TWX5024A1000A (2-ton XL15i) with the 4TEE3F39A1000A yields 13.00 EER, 16.00 SEER, and 9.00 HSPF. The 4TWX5018A1000A (1.5-ton XL15i) with the 4TEE3F31B1000A (only rated match with the 1.5-ton outdoor unit) yields 13.00 EER, 15.00 HSPF, and 8.50 HSPF. Feel free to print out my responses if it will be easier for you to go over these possible issues with your contractor. Good luck.

It was indeed stolen. The property was bank owned and they had to get it to a habitable state to sell to regular homebuyers so installed a new one. The problem is the contractor installed a brand new air handler, thermostat and condenser onto an existing drain line and lineset. The AC apparently worked while being tested and was then left as a completed job. I bought the house and started the rehab. Straight away it kept cutting out or blowing warm air. It turns out the drain line was clogged which stopped condensation draining so a float switch kept cutting out (this took a couple of visits and a new float switchto figure out). But there also seems to have been a second problem with the line set, as whatever work is done (so far a new float switch, new second condenser, a new second compressor, a new evaporation coil...) it hasn't fixed the problem of the ac running and running and blowing warm air. My question is, am I expected to pay for a new lineset if he installs one as another attempt to fix this 4 month problem? So far it has all been under warranty.

It's not how much you're drawing from the grid but how much you are drawing in total. This assuming that you load balance (grid + solar) before your panel which is typical. (The other option would be to have one panel for grid connected circuits and one for solar connected circuits but I'd recommend against that.) Also, there are still likely to be cases where you will be 100% grid unless you are OK with not having some electrical things available when solar+battery is not available. So, I think you will likely still need a panel capable of handling the entire electrical load of your house in order to meet code. I believe Span uses standard dumb breakers and just has their electronics behind it. A significant problem w/ new electrical panels is AFCI nusiance trips (think having to reset a breaker once per week or day). Some panels such as Square D's new stuff are doing a much better job than others such as Eaton or Siemens so something to think about.