They have to be vented out of the window but there is no danger of anything falling as your tenant stated. https://www.goodhousekeeping.com/appliances/g21286604/best-portable-air-conditioner/?

Do you install an air conditioner or a dishwasher?

For example, having multiple air conditioners or space heaters running for long periods on the same 15 amp circuit.

From hot water heaters, to air conditioners, to roofs, etc - so note the condition of all the major systems in each unit.  

I have been told that my air conditioner "The system unit needs to have Freon up to 8lbs to 9lbs and replace Coil Condenser.

The heat was very high recently and the air conditioner above unit had some issue and the water dipped from the pipe of that unit and damaged my unit.So I requested clarification to my property management company how they provided a quote without identifying the root cause, but haven't got any response yet.

Is is a big safety hazard to plug a 5000 BTU air conditioner into a heavy duty 6 ft or 12 ft extension cord and then plug that extension cord into the wall? 

For instance I needed a wall air conditioner picked up and installed while I was on vacation he picked it up and installed it.

That is an $8400 per year increase in gross income, or $84,000 in 10 years and that is how you need to do the math.I don't have to remodel the unit, but it has a 1960's kitchen and bathroom and I like to re-wire the units with an upgraded electric panel, 110-volt smoke detectors and I always install an 18,000 btu air conditioner through a wall (not in a window.

I have learned a lot about maintaining an elevator, fire alarm system, public restrooms, boiler system, commercial air conditioners and most of all the different laws for commercial tenants vs residential tenants.