Two Central units
Its hard to say why, you would have to ask the architect or mechanical contractor, but normaly its one of three things;
1.) Space, could you imagine trying to work on an air handler in such a small space.
2.) Load requirements, they may have wanted staging that a single air handler could not provide, is the condo zoned, or have VAV or VVT. Remember that when the units are twinned, measure total CFM for smoke detector requirements.
3.) Money, in some instances it is less expensive to instal two small units vs. one large air handler.
Normaly both fans operate together and the heating and cooling are staged. Rarely does everything come on together. One unit will be the "master", the other the "slave".
If you have access to the Carrier Portal, or the Lennox site search "Twinning Kit".
I would be more than happy to come down and help you with this, even more happy to come down in January! Thats from the heart dude.
Last edited by 8 Ball; 09-07-2008 at 10:16 AM.