"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.

I immediately installed a dishwasher and multi-split air conditioner in the upper unit and found tenants to move in and help pay the mortgage.

Lessons learned - If there are window air conditioner units in an eight year old house with central air then your evaporator coil is full of cat/dog hair and your compressor is bad.

Since 2006, I replaced all three bathrooms in the house, refinished the hardwoods, rugs, hot water heater, air conditioner, added pavers in the rear patio, replaced all windows and the list goes on and on as I’m sure everyone can imagine.

Something simple like a water heater or air conditioner?