mimisma,

One thing to ask about is the "SEER" rating (Seasonal Energy Efficiency Rating) The higher the number the higher the efficency. Ask if the equipment qualifies for a rebate or tax credit and if you will recieve it. Ask about the controls; programmable thermostat or not? the more vague the estimate the more latitude the contractor has to "Change the deal", so you need to have everything "In Writing". Ask for three references, a copy of their license and insurance information. Check with the better business bureau to see if this contractor has any unresolved complaints against them.

These are some of the basic things to ask about whenever you have a contractor do work, some of the finer details a homeowner sometimes just has to trust the contractor. If you did your homework right with the basic questions, the finer details should fall into place.

Hope that helps!