Which central split pack unit should I buy?

My friend is in dire need of help. Hopefully someone can help her with this costly decision. Here's the info:
She lives in a ranch type house with full basement of approximately 1500 sq. feet. Her central air unit has died and she is going to buy a new one, however she has talked with so many air conditioner installers she is now confused.
Some have recommend an Ammana, 18 seer unit, with 2 compressors, 3 ton unit. Another has suggested a Trane 18 seer unit, 2 1/2 to 3 tons. Still another has suggested a Trane 13 seer unit, 2 1/2 tons. What is in the house now is a 2 1/2 ton unit, Comfort Maker and she has no idea how many seers it is as it is 18 years old.
Most have suggested the new refrigerant R-410A and all the units they have recommended has this except the 13 seer unit.
Does anyone have anything to add to what she needs, any recommendations, pros, or cons??? She would really like some help in this uncharted field.
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snipped-for-privacy@webtv.net wrote:

Anyone that recommends an AC based upon the minimal information that you have given us should be ignored. The AC size depends upon many factors such as climate exposure, windows, insualtion, etc. Find a contractor that will do a manual J load calculation. Also, there is no Trane 18 SEER R-410A AC in the capacity range that you mentioned (only R-22). That may also be true of Amana, but I don't know.
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Well, I'm sorry! We did not what kind of information was needed. She has new triple paned windows. We know for a fact there is an R-410A for an Amana, go to their website. As far as climate exposure we are in Middle Tennessee, right outside Nashville to be exact. Very good insulation in the house, too. Now can you give us a civil explanation without biting our heads off???
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wrote:

they did. the pertinent lines are

we can't see the house, nor calculate this, over the internet. you need someone locally to do this.
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wrote:

He already has...
Find the best installer you can find that will size the equipment by performing a manual J. Than make sure the ducting is adequate by performing a manual D. Make sure they don't do any shortcuts, because you want it done cheap.
Equipment brand is meaningless without a qualified tech to install and set it up properly.
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I bought a AC system and gas Furnace a few years ago. Being new to the town my choice was based on CU ratings and experience of friends that live a couple hundred miles away. The only local dealer for this brand had been in business for over 100 years in plumbing and heating and was a fixture in the community. Three years later I finally found a service tech for a new dealer who finally get the thing working. I remember buying two computerized controllers myself in addition to the three or four that the first dealer went through. Lesson: buy by dealer, and only after many good recommendations.

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