If your goal is to generate passive returns, real estate (done properly) may not be the right vehicle. 

He charged me $2k to purchase and install a 75 gal gas water heater, and dispose of the old.

I got quotes from 4-6k to install central air. 

When you say "seperately metered" do you mean installing furnaces for all four units?

I would contact an attorney that specializes in evictions or find a and handle this legally and properly.

One possibility is install a window unit or get a porta cooler at no charge to them. 

Just installed some last week, and they're nice, solid, have great hardware, had a thousand different options available, and are warranted for a really long time.

I had Permabuilt install 6 piers maybe 6 months ago and had a pretty good experience.

And even pre-approvals must be worded properly and followed up with the appropriate changes to the Financing Addendum so that what happened to you this time won't happen again.

Anyway, I am trying to maximize returns and run things better now that I am setup as a real business tracking everything to the penny, following proper LLC safeties, and added 4 more units, etc.