If you're gutting the entire place: then I would put in furnaces with air conditioner and dedicated ducts/systems for each unit.

One water heater or refrigerator or air conditioner or water leak and suddenly you have a zero or negative cashflow situation. 

One had a missing air conditioner (stolen) which I didn't anticipate.  

@Glenn Primack, having too much cash buildup is certainly one of the better problems to have with your business.Upgrades can be from a mild aesthetic upgrades (refresh paint on the trim / light posts / mailboxes), more expensive renovations (landscaping, new garage doors, new air conditioners in units that need them), or major projects.  

I paid $3,300 for furnace/air conditioner (excluding duct work).

Are there air conditioner units in this building?

They had some ideological goals and that suited them.I know we rent out a house in which we replaced an old boiler and air conditioner and cut energy use by about half and the biggest results we've got to show for it are much lower maintenance bills from the new equipment and stable renters that turn over infrequently.

When I arrived, I found that employees from the cleaning company that were contracted by Fannie Mae had stolen the water heater, air conditioner, and the furnace. 

Same problem once with an air conditioner repair guy.

In Texas, an air conditioner repair generally does not fall under this category.