That HAS to be because it is leaking.

Is there a leaking sprinkler or drip system?

cast-iron drain plumbing that is end-of-life and leaking?)

It includes:Office contact informationHow to report maintenance How to report maintenance after-hoursEmergency numbers (9-1-1, gas leak, etc.)Location and size of air filter, water filter, etc.Location of water shutoffLocation of gas shutoffLocation of Breaker BoxLocation of sprinkler controllerAny unique instructions for the property (how to use jetted tub, how to prime sprinkler pump, etc.)I provide additional information on my website or Tenant portal for those interested in learning more about move-out instructions, how to add/remove a pet, how to terminate a lease early, etc.

Restricted air flow across those surfaces increases energy consumption and puts unnecessary stress on the moving parts.However, A/C systems are sealed systems and should not have to topped up or recharged unless there is a leak.

Are you certain you don't have a leak ? 

It's really hard to find a company that is good.....and by good I mean they repair any plumbing leaks the cause, they can do minor electrical diagnosis, and things like that.

@Ali Croft if you use an iPhone, there is a Flood Zone app that works really well. https://apps.apple.com/us/app/flood-maps-zds/id908554933Try to stay out of the flood zones for investment properties. 

Camera - Seriously, an iphone is perfect for this until you scale.3.

@Sasha Fukuda When water leaks from above, it will get between the subfloor and the ceiling of the downstairs unit.