in the middle of doing the same thing. I took 4 bids and I don't claim to be an expert, but I learned alot in the process. The good vendors are VERY good and work hard at assessing your needs, but it is a jungle out there. One of the bids was from the big orange home store installer......the rep showed up w/o busineess card or product information. Recommended a size and unit without so much as a hard look at my current system..I sent him packing. Then I got bids from 2 Trane dealers and 1 American Standard dealer. The trick is getting apples to apples comparisons. That means same/equivalent models, seer rating AND tonnage. A reputable installer will measure your house/windows and take into account how much you will lose from heat sinks (whole house fans, attic stairs, etc...) and run a J load (sp?) calculation. What I found is some will quote a price for a certain XYZ Seer rating and model then sell you on tightening up your system (at a cost to you....sealing duct work, stair zippers etc....) the set you up with a lower tonnage system......now that is fine and well and probably a very good idea, but the lower tonnage should mean a reduction in cost but....some will try to hold to the original estimate. As a test I asked one vendor the cost of going up on tonnage within the same model and seer rating.....he stated a cost increase. All will guarantee if the system they install isn't cooling properly they will upgrade at no cost......but how will you know? Like me you have a 20+ year old system that is an energy hog. By comparison, most any 13 seer unit will be a vast improvement, but how will you know if it is working too hard to keep up? Just some things to think about, I hope it helps. Hopefully someone here is in the business and they can provide better insight.
-SG
FYI: American Standard OWNS Trane, they are the exact same equipment, different labels. The load calculation is called a "Manual J." Most companies don't have a clue how to do them: and there is a 99% probability that the guy who comes out doesn't either, because he is a commissioned salesman, not a licensed individual.
SEER 13 is the new federal standard for the minimum SEER rating. If your AC just went out, go ahead and go with the 410A refrigerant. R-22 equipment will no longer be made after 2010 (replacement parts will be) and most manufacturers are starting the transition now.