I have two A/C units (1 @ 24 years and 1@ 16). I want to be prepared to make a good decision about replacement units when the time comes. I don't want to make that decision when the house is 101F and my wife is upset.

What questions should I be asking contractors now so I can review their input in the cool of my living room?

I have 2300 SF and it is divided into two areas by a door. I heat/cool one during the day and one at night. Living area is kept at 79F and bedroom area is kept at 75F.

Current cooling costs are about $70-80 per month during the summer in the Dallas area.

Thanks for your inputs.