But then we turned on the air conditioner. 

So, like a window air conditioner, but installed in the wall instead of a window?

You might ask your bank how long you have to own the duplex before you can get an equity line of credit on it - you might be able to finance the systems through the HVAC company, pay that note for 6 to 12 months, and then pay off the HVAC company's 18% loan with 6% money from your equity line.Right now, every HVAC company is busy fixing and swapping air conditioners. 

That is like saying a broken air conditioner in the middle of summer and a inoperable doorbell should be handle with the same level of priority.

They're going to put Air conditioners in during the summer anyways, I'd rather an efficient one running if I could then one I can't control what it is. 

I had a tenant at the beginning of summer that said his air conditioner wasn't working.

Clean the air conditioner condenser outside.

In fact, one tenant downstairs, who's an undercover narc, had his apartment broken into by someone climbing through the opening in the wall for installing air conditioners.

Yes the duplex has only one roof, but it has 2 stoves, 2 refrigerators, 2 air conditioners, 2 furnaces and most importantly two tenants!

The neighboring building (mix use commercial) recently mounted what appears to be a large air conditioner unit on the side of his building 2-stories above ground.