There is also reserves to consider… like “can you cover an AC  air compressor going out in the same month as a hot water heater and still pay your mortgage?" 

(Bonus depreciation is usually better than deducting it under de minimis.)The other two pieces are furnace and AC, compressor I assume, both parts of the HVAC system.

We have 37 units, and our typical rental would not meet that threshold to be worth it in a year  Yes, there is a chance your AC compressor could go out and you come out on top where the warranty was cost effective… but in my experience it is unlikely - and the frustration isn’t worth it.  

Proper ductwork (aka no leaks) will increase the life of your compressor as they are rated by how many times they turn on and off.

Nothing bigger than a small radio is running on the receptacles.We had a compressor running on a different circuit, but this never happened when it was running.

Being battery powered you don't have to be tied to an air compressor.  

HVAC has AC trouble in my rental unit, the guy said the compressor is locked, he installed hard start relay and says doesnt know how long it will hold up, compressor is noisy as per him and cant be replaced since it doesnt have compatible freon so I need to replace the system.

Ed LeeIf you have an efficient gas furnace already and the heat is forced air, you can add a central cooling unit into the plenum (with an external compressor like a heat pump) to provide central air to the building.This should be a more cost efficient solution than replacing the existing system.

The strange thing is, it doesn't trip all the time, so the repairman said it needed a new compressor.

Total 4500. 6500 with a compressor.