The blower of the unit, both operating as a heater and as an air-conditioner, sucks up air from the returns and expels it through floor registers.

the air conditioner, or the home?

Lets be honest about what happens to cash flow of a couple of hundred of dollars a month when you have to replace an air conditioner for a couple of thousand dollars.Rent per square foot in Honolulu $4.36, Vegas per sf $.78.

Clogged Drain Plumber Plumber Furnace / Air Conditioner LocksmithElectrician

I considered buying one in a nearby area a few years ago for my first home, but quickly learned there are a lot of additional costs for things that would already come with an existing home, such as air conditioner, blinds, etc.

A neighbor (who has a tenant living in their unit as well) 2 floors above's window fell out and crashed onto my tenants' brand new window unit air conditioner and her car, damaging both. 

Also built in an air conditioner, which is a must in Thailand.What was the outcome?

I think that given that the former tenants gave you back the keys and the text message would lead a reasonable person to believe that they abandoned the property left in the unit (much like stuff left in a unit after a lease expires -- it seems like I am always throwing out a stray bag of ratty Christmas decorations that I assume have been abandoned).I think the safe way to proceed would be to text the former tenants with a date and time when those items will be removed from the unit, along with a request for them to return the air conditioner.

Eventually (like once we marry, have kids and need more bedrooms; 2-5 years out), we will move into the main house and rent out the carriage house.There is already a poured concrete pad and hookups outside for an air conditioner, probably a compatible thermostat in home already.

Here in Texas its really the Air Conditioners.