Thanks,Ana @Ana VhanWe own 40 air conditioners between all our properties.   

The air conditioner manufacturers are going the way of the automotive company's so you have to use their parts on newer equipment coming out.

Sound penetrates with doors and windows closed and new air conditioner on.

For example, if the HVAC is now one system, what happens with the cost of replacing the outside air conditioner unit but not the entire system (same furnace, blower, vents, etc.)?  

The condo has a refrigerator, electric stove, and window air conditioner.

Also, an Air conditioner will work more efficiently if there is less moisture in the air (Houston, Florida, Alabama, etc).  

This apartment building has 12 units and has some very old central air conditioners that will all likely need replacing at some point.  

If you have an air conditioner in Arizona blow up  in the summertime (like I have), you need to have a Plan B, C and probably D.  ;-)Warranty Companies 'Suck':  Yup, some do.  

For example, one apartment upon inspection had an air conditioner set at 60 degrees and on the max level when only their dog was home. 

I don't know if your property has a fireplace, but to add to @Michael Greenberg's set of rules, which is very similar to our set of rules, we add "we ask that you please do not run the fireplace and the air conditioner at the same time" Because that costs us approximately 1 million dollars in electric bills.We have the same checkout procedure: strip the beds and put sheets/towels by the laundry, run the dishwasher, take the trash to the outside can.