There are so many factors to consider the "ONLY WAY" to know for certain is having a compitent technician evaluate the home as well as the system. Rule of thumb which sound's like how it was done,properly installed 3 tons should be adiquate if everthing about house is as it should be.

Undersized is much easier to fix than over sized. If after you have the system evaluated and if that checks OK, then you could work on reinsulating the house, starting in the attic.

Very easy to drop the load a 1/2 ton by adding insulation to compensate for your smaller unit. It's best to use blown in insulation in attic to seal around all cracks and crevices. The cheaper the insulation, the more likely it is that it will have to be redone again at a later date because it is 'puffed up' with mostly air and it will lose this puffed up thing over time as it settles.

It is possible you may have both problems due to the age of the house. So if there's problems with your AC system you should address those first.

Let us know what you find.

It seems that system is doing its work. It brings down the humidity significantly which means coil is cooling properly. Blower is maintaining set airflow of 400cfm. I will call the installer and see what he has to say.

A larger unit running shorter cycles won't necessarily result in less energy use. Larger capacity draws more power when running, and oversized wouldn't reduce the humidity as much which leads to turning the temp down to compensate.

Before you do anything, refrigerant charge should be checked, supply temps should be checked, temperature split should be checked, and ductwork system should be checked.

IMO

Yes, call the original installer and let them know the system isn't performing as expected. 3 tons should be plenty for 1600 sq ft.

And I assume you mean 400CFM/ton (ie 1200cfm total)

nationwide the average house has 30% duct loss.

your 3 ton system likely is only delivering into the living

space 2 tons.

mastic seal the ductwork, plenums to equipment, return air

& each supply box penetration.

this will make a difference for a small material cost

(but high degree of difficulty of sealing) it is an

investment that is well worth it, fast payback...

immediate difference you can feel.

before blowing more insulation in the attic,

air seal the attic floor, mastic seal ducts as above.

then once all attic work is completed, insulate.

avoid cellulose as it produces a fine dust that finds

its way into each small opening into the living space below.

it is better for the system to start up and run for a long time.

longer run times remove more humidity.

the start up of the unit is what increases utility costs.

once it is running it costs very little to operate.

oversized systems are common, but create issues

above in addition to having a shorter life due to

excessive starts.

best of luck

Yep, a lot of things to consider, but here are a couple of things to consider.

1. Regardless of construction, a 3 ton system will be close for a 1600 square foot house. It may be that your system is undersized but check a couple of things first.
2. Your ductwork. I don't know how contractors work in IL but in TN, we are notorious for undersizing ductwork. System capacity is a product of temperature difference across the evaporator coil AND air flow. If your airflow is under what it should be (about 1200 CFM on a 3 ton system), you will not be getting 3 tons of capacity. Talk to a knowledgeable HVAC contractor that knows air flow. This may be a better use of money to fix the problem than jerking new equipment out.
3. Installation. I know it sounds silly, but the installation is 90% of what causes a new system to work properly or to NOT work properly. It's late in the game to go back and get mad over the installation, but if you suspect the installation is sub-par, you're probably right. If you got 3 "bids" and selected the cheapest bid for the installation, the installation may be the problem. The way the system is installed is always the key to correct capacity and efficiency.
4. The newer equipment will not always produce the "nominal" capacity. In other words, a 3 ton system (36,000 BTUs) may not produce 36,000 btus by the manufacturer's catalog. Just a thought.

For some articles I wrote on installation, duct systems, and efficiency, feel free to see MY BLOG.

Air and Energy: Man are you in the wrong forum. Here the recommended choices are often Trane and the lowest bid possible.

'Talk to a knowledgeable HVAC contractor that knows air flow. This may be a better use of money to fix the problem than jerking new equipment out.'

He would have to be really nice to stick his neck out on a HVAC system that he didn't install. Does Trane offer any Atta boys? - nope.

#Why it's so important to do it right the first time.

I'm afraid you're probably right. The same is true here. Trane has done a great job of selling "boxes" to unqualified service contractors eager to sell a box. I'm probably a little jaded since I'm the guy in our area that is usually called in after all other options have been exhausted and the installing contractor is nowhere to be found. I'm also the guy that rarely gets the job when two other contractors are "bidding" on an install, and usually don't even submit a bid. Our job, as contractors, is to try to educate homeowners and building owners as to how important proper installation is. Unfortunately, the attraction of a cheap installation is more than most of us can stand, and this is where we end up. By the by, I was so irritated yesterday I had to write another blog entry dealing with this very topic. If you're interested, HERE it is. Let me know if I can be of any further help (or discouragement).

On a side note, I noticed santu mentioned "all of the contractors". It's too late for this time, but I think worth mentioning. I don't mention this to hurt anyone and I'm not insinuating that I know this is what happened but from my perspective, this is where we are as a society. We live in a Walmart / Chinese crap economy where our first instinct is to shop around to find out who can provide anything we need as cheap as possible. That works great if we're shopping for a GE model BR549 widget that is the same widget at Walmart as at the local hardware store or super warehouse. It's a commodity. Service is different and somehow we have to learn how to communicate this. We have different skill levels, different levels of integrity, and different levels of concern for customer satisfaction. The bottom line is this; find someone you trust and use them exclusively. Sorry for the very long explanation and for getting off topic a little, but I think this is critical for homeowners.

The problem, Air and Energy, is that for the average homeowner, choosing an HVAC contractor for a major project is a rare experience. Some never have to do it. And when it's teed up to get done, it's hard to know who to believe and what factors to base a decision on. Scoundrels can look as presentable and have the same references as the saints.

(Your comment above that 3 tons is marginal for a 1600 sq foot house, knowing nothing more about it, isn't confidence inspiring to me, from what I've learned from my own experiences in HVAC-land)

Thanks for your comment and I understand completely. As far as the 3 ton it may be fine. I only mentioned that because I ran a Manual J for a customer a few months ago with a 1400 sq. ft home. The heat load came up to 2.95 tons. I opted to go with a 3 1/2 ton system and he's very pleased, even on days that hit 100 degrees and he tells me his electric bills are lower than they have ever been. You may not have that problem there so my comment is only something to think about.

Oh, and yes you're absolutely correct. The scoundrels can sometimes look even better than the real thing as they are better actors than contractors. Sad but true.

Thanks again.