I design and manufacture air conditioner cages.

If you don’t have these kinds of funds available, how do you expect to fix an air conditioner when it breaks or solve a leaky roof issue, or pay the plumber that comes out at 2 in the morning on a Saturday night to stop the flood in your basement?

Cost $7k.2) The central air conditioner and furnace are original.

I have seen that for Floor coverings and wall air conditioners but other items could be in that category. 

"Heat pump" air conditioners provide more consistent cool temperatures throughout the house and remove a lot of the humidity in addition.  

It should be as simple as calling them up and asking to add on another meter.I would keep it as a triplex and install a window air conditioner in the other unit. 

Air conditioner units in windows.

Here in the east, with heat waves and humidity, it is common for most air conditioners to cool down between 10-20 degrees below the ambient air outside.

:(I don't really need A/C but I thinking of using the a wall mounted Ductless ( Mini Split ) Heating / Air Conditioner with an external unit as a replacement.If I get one of these then I would seal the floor furnance.Anyone, have experience with these ?

More over, she failed to upkeep the house, she turned off air conditioner and leave the window open to save money.