Why mate one condenser to a variable speed furnace and one to a non-variable speed furnace in option 2? Doesn't make much sense to me without hearing any apparent reasoning. I like to see variable speed furnaces with 2 stage outdoor units, even though the boost furnace (which just has a high efficiency, non-variable motor) may be a rated and approved match. Just my opinion. If you went with option 2, I'd ask to have both furnaces to be variable speed models (58CVA090). Which thermostat is quoted for both options? Should use Infinity control for option 2.

Tigerdunes, Thanks for the prompt feedback! I'll ask the contractor about the heat strip. (Our winters are very mild so I was more concerned about the A/C.) I agree, the utility company should not dictate size, but what can I do about it? Do you think I should instead go with a 2.5 ton unit and forgo the $400 rebate? The contractor agrees though that a 2 ton unit would be fine. My house is in the shade from post oaks, all the way around all summer long. Perhaps that is why the old system lasted so long(?) and the contractor thinks 2 tons would be OK. I asked him about the lineset (after reading about it on the forum). I forgot to write down whether he was going to flush them or replace them. I'll ask again. Should I ask that he replaces them? For the last decade he has mostly installed Rheem systems and tells me he has had excellent results. Thanks again.

You have a contractor problem! Here is my suggestion. First, change your approach. Stop playing HVAC contractor. I understand feeling the need to based on how your contractor is responding, but stop, now. Escalate the problem to the local Carrier distributor. They have at least one dedicated technical advisor on staff to help a contractor who is struggling, and your contractor is clearly struggling. (Sidenote: You distributor will be either independant or factory owned.) Monday morning call the distributor. Calmly tell them you bought a brand new Carrier system x weeks ago from x contractor. It has never worked correctly. They have been out x times since the installation and they don't seem to know what to do. A good distibutor will jump right on it. First, he will talk with the contractor to review what has been done so far. He may suggest a course of action for the contractor to take or decide he needs to see the installation first hand. Push to have him see the installation. Also, confirm this is the distributor's dedicated technical guru you are dealing with and not the distributor's sales person who sometimes is dispatched to go out and smooth things over, ultimately hoping to explain away the problem. Be nice, but firm. Good luck. If you get any push back, and hopefully you won't, point them to the link below.

mike_home, you make the perfect argument for why Manual J should be mandatory for all HVAC contractors. It would protect the customer from hacks and unscrupulous contractors. Smaller equipment means less cost for electricity over the life of the AC unit and less cost up front which saves the buyer money. The electricity savings is why the utility companies and many states are making it part of their mandatory requirements to have their HVAC contractors perform Manual J. Here's a good explanation from Dean Heating and Cooling on HVAC Talk Forum that explains the benefits of using a Manual J and also talking about proper duct design (Manual D). "A load calculation known as Manual J is the only correct way to determine heat loss and heat gain. Once equipment size has been determined, the duct system is designed by Manual D. These are design protocols formulated by ACCA. Duct design takes into account the location and potential gain (or loss) of having ducts in an attic, crawlspace, or even exposed on a roof. You are correct the installing a larger air conditioner on an undersized duct system is pointless. We have all seen it many times. Frequently, putting in smaller equipment delivers greater comfort when the existing equipment is too big. For example, a 4 ton unit on a 2.5 ton duct system can only deliver 2.5 tons worth of air flow. The oversized equipment still uses the electricity for 4 tons of cooling but the delivery system still limits what arrives in the space. The equipment actually uses more energy because of inadequate air flow. Plus it cycles more often than smaller equipment so its life is shortened." Here's a good discussion about Manual J calculations also from the HVAC Talk forum. There's an HVAC designer and an HVAC contractor that post over there that seem to have the most input on Manual J. Their user names are "dan sw fl" (AKA Designer Dan) and lkapigian.