Thanks all! I am learning a lot. The reason I am thinking it is coil that is leaking is because the AC guy who performed initial diagnostic last Spring used some kind of a device which looked to me like "electronic leak detector", according to the posted description. At this time, I don't have a reason to believe he did a bad job last year. He poked his instrument in different places. One of the places that (according to him) showed the "leak" was the coil (which was, by the way, located inside the furnace cabinet in the basement, not outside.) The reason I am not completely sure about the diagnostic is the following. He said that according to his instrument's reading the leak was pretty minor. That's probably why he recommended simply recharging puron. However, the puron he put back into the system apparently leaked out over the course of last summer. So maybe the leak at the coil was not so minor in the first place? Or it could be because there was more than one place where the system has a leak? Anyway, I am going to call a different company this time. Based on the info I have so far, the coil might be only part of the problem. That's why I try to keep an open mind and consider alternatives. Yes, I read that 16 SEER is a minimum rating to qualify for tax credit. My concern is that I already replaced the gas furnace not so long ago. Can I pair my furnace (Carrier 58CVA110-20) with another modern Carrier AC unit of 16 SEER or higher so that they work seamlessly together? If yes, what model would match my Carrier furnace? If a new (comprehensive) test confirms that the leaking coil is the only problem, how much I should be prepared to spend on fixing it? The company that quoted me the price of ~$1600 last Fall told me that they would have to first evacuate the puron from the system (which is expensive), then replace the coil, and then put another load of puron into the system. That's why it is so expensive, they told me. Does it sound right? I've seen quotes for complete AC system installs at around $6K. Considering what I have to spend on diagnostics and repairs anyway, plus accounting for $1500 tax credit, I figured I will end up only couple of $thousands short of being able to replace the whole AC system... Or am I missing something and the difference between repairs and replacement is actually a lot more?

Your existing system is either a 10 or 12-SEER unit; they were good performing units, & a new one, especially if oversized may not produce any savings over the older unit. A 3-Ton properly installed & setup unit should cool your 1700-sf home at your location. You can always do cost effective things to reduce the heat-gain. It is all in how well everything is design-engineered... In fact a 2.5-Ton unit might cool it; that is only 600-sf per/ton of cooling. I cool my farm home with a mere half-ton window unit for the entire 1st floor; that's around 1200-sf per/ton of cooling in very hot & humid weather extremes. Slightly less than a half-ton upstairs -.cooling 2 bedrooms a bath room & hallway; usually only run it for a while before going to bed unless a real hot day & night. A 5th grader can perform that LINKED load-calc print the instructions & follow them! Here is a link that might be useful: Free Whole house Load-Calc

My current system has the Carrier thermidistat, that can monitor temp and humidity, as well control the HP and Furnace, or at least I think it can. I am not sure where the programming for switch points and such are in my current system, I was a lot more trusting back then. As far as the duct work I know the supply duct work was redone with the last system and increased in size greatly. The one contractor did check under the house to take a quick look at the ducts. The reason I was given for the high install price of just the HP and coil was that they would have to uninstall and re-install the furnace to perform the installation. Then it just became the cost of the new furnace while doing the work. I thought it was very high but the quote have all been what I thought to be very high. I know that I have been concerned about the sizing, as it seemed quite large. I have asked the one contractor about the furnace size and he is going to look at that. He did tell me that they usually just match the furnace to the HP, at the same size since the cooling is more critical here. Also, the furnace can modulate down to a lower capacity to save energy and keep the comfort at a certain level. I have a feeling that the contractor is frustrated with my asking lots of questions, but I try to be an educated consumer and this is turning out being a larger purchase that expected. I know that I have tried contacting 3 more contractors and they have not returned the emails or calls, it has been 2-3 days now. I am not sure how far out I should look for a contractor, Raleigh is about an hour away from me and not sure how many would be willing to travel for the job, or how responsive could they be if a problem arose. I appreciate everyone's insight and advice.

OK, folks, I met with the owner of Fort Collins Heating & Air this morning. He seems to live up to his reputation of being a stand-up guy. I told him that I was going to talk with him this morning, then with a competitor this afternoon, then get back to both of them tomorrow morning with a decision. So I would massively appreciate your thoughts on which course of action to take. I told the FCHA owner that if I decide to keep my existing system, this is what I would want them to do: Have their best team replace the humidifier and go over the system from top to bottom. Replace the thermostat, too, if they can't make the low-battery symbol go away, given that I just replaced the batteries last week. Extend the first-year tear-it-out warranty to March 30, 2019. No charge for repair calls from now to March 30, 2019. Free furnace inspections in Sept. 2018 and Feb. 2019. If I want the system torn out with a full refund at any time between now and March 30, 2019, FCHA tears out the system, no questions asked. The FCHA owner said he's pretty sure he could agree to all of those conditions. I then met with a sales guy from another HVAC company that also has a solid reputation. Here's his proposal: 96% up to 97% 2-stage heating, variable speed motor. 16 SEER A/C system. 1-stage cooling. : Installation to include: Finish the mastic sealing in the mechanical room per code. All necessary PVC venting needed. All 220v, 110v, and 24v electrical needed. Condensing unit outside. Evaporative coil inside. TXV (thermal expansion valve). Refrigerant lines from inside out. All installed. Task HCS-PH60. Premier Amana Two-Stage variable speed gas furnace. 96% AFUE. Stainless steel tubular primary heat exchanger. Efficient and quiet variable speed circulator motor. 10 year parts and labor warranty. Limited lifetime “unit replacement” warranty on heat exchanger. *Annual maintenance required. Price: $6,682 Task D-F750 $750 off high efficiency furnace Task HCS-DC30. Deluxe Amana high-efficiency air conditioner. Up to 16 SEER. High-efficiency scroll compressor. Single-speed condenser fan motor. Limited lifetime “unit replacement” warranty on compressor. 10 year parts and labor warranty. Lifetime limited “unit replacement” warranty on heat exchanger. *Annual maintenance required. Price: $6,024 Task D-AC750. $750 off high-efficiency A/C Task HO3. Bypass evaporative humidification. Can be installed on supply or return. Works only while heat is cycling. Not recommended for home over 2500 SF (My home is about 3,800 SF, including partially finished basement). Price: $895 Task D-HSHUM. Free humidifier with purchase of high efficiency furnace or AC system. Task ACO4. (Air cleaner, I assume). Honeywell 4” disposable air filter. Merv 8 filter rating. Uses no electricity, but requires replacement media quarterly. Price: $895, but free with purchase of high efficiency furnace or A/C system. 5 year parts and labor warranty. Task TS-EC4. (thermostat/humidistat, I assume). Comes with built-in Alexa Voice Service, so you can ask your ecobee to set a timer, read you the news, etc. 5 year parts and labor warranty. Price $0.00 Task ACO7. Return air box (square – 14, 17, 21, 24) includes easy 1” filter access. Improves air flow efficiency by up to 25%. Price: $0.00 Task SD-100. Senior discount. $300. Cash or Check discount. $100. If I have it installed 3/8/18 (may not be feasible): $350 discount. Total: $10,566 All of this partly depends on the current supplier leaving all water supply lines and electrical. Otherwise, it may cost me about $500 more, according to the sales guy. Given your HVAC knowledge, what would you do if you were in my position?