My parents in Miami need a new AC. Their house is split between 2 systems...a 2 ton York for the bedrooms (approx. 800 sq. ft) and a York 2.5 ton compressor/3 ton air handler for the living area/kitchen (approx. 1200 sq. ft.).

The problem is that the living area never cools down below 78 in the heat of the summer and the unit never shuts off during the day. This area includes 3 sliding glass doors and 2 windows that face the west.

The contractors insist on changing the units out with what is already installed since the original contractors already sized it. Well, I disagree, but noone wants to do a Manual J or load calc and only take square footage into account. Man, you should feel the heat coming through these windows in the summer with the shades closed!!

Anyway, should I just tell them to install a matched 3 ton unit even though it might seem like overkill for 1200 sq ft.? Will humidity be a problem? Should I pay some one to perform some kind of heat load calculation? None of the contractors offer that. They just want to install a system and be done with it.

Sorry for the long posting...