The fix for that is usually shutting off the power at the box on the side of the house where the cable from the A/C connects, hosing it out with a garden hose (use a wide spray nozzle rather than a thin "laser beam" of water, so you don't bend up the fins on the condenser), letting it dry out for a couple of hours, and then turning the power back on. 

This might be a good place to condense everything you're learning in one area, then branch out to other topics.

Problems can obviously arise in SFHs, but, say an HVAC starts leaking condensation, one property will be effected instead of 2.

But if the source of the mold, like a water leak, condensation from an HVAC, or roof leak is not fixed, it will just return.

Clean the air conditioner condenser outside.

Keep your condensation pumps in good working order (occasionally pour in a SMALL amount of bleach or other agent to kill algae , make sure outside tube not blocked / clogged/ kinked / frozen )

Great ideas above, just to condense everything and add a couple more ideas:Low flush toilets and Low flow fixtures (showerheads, etc.)LED Lights and more energy efficient common area lights, if applicable.Replace windows with energy efficient windowsImprove insulation in the attic and crawl spacesRecaulk windows and make sure all doors are sealing well when closedUpgrading appliances, water heaters, etc., if they are extremely energy efficient.If higher quality property, consider installing nest thermostats to help with energy savings since tenants won't care if they aren't paying the billI'm sure there are many more but those are a great place to start and get the bulk of your savings. 

As opposed to naturally occurring affordable housing or workforce housing, targeted affordable housing means the property has rent or income restrictions in place to maintain affordability for an extended period.Through the TAH Express program, borrowers benefit from a condensed prescreening process, simplified nonnegotiable legal documents and a standardized underwriting process, resulting in lower transaction costs.

When you say HVAC system do you mean just the furnace or the evaporator and condenser too?

The challenge is they did not identify the source of the leak and the landlord is blaming us for condensation on the shower door leaking onto the tile floor and seeping into the wall.