Size A/C system properly
something doesn't sound right with your estimated R-value.
hot in the day and cold in the night? with an R-value like your describing, this should not be the case.
Typical installation here in chicago for your home would be 3.5 ton. Your contractors need to take a good look at the sheetmetal to ensure that it is sized properly, and that the furnace is sized properly as well.
It sounds to me that you have built an addition without spending the money on properly changing the furnace and sheetmetal to accomodate your new load. even with a new properly sized A/C, you will still experience these problems until the whole system is properly sized to accomodate.
simply just tapping new runs off of the sheetmetal that was designed for the 1300 sq ft home will leave you with the exact problem that you are describing. an addition like that would have led you to replace the whole system, or add a new system with it's own unit for the new addition.
Last edited by Aceinstaller; 03-26-2006 at 08:26 PM.