However you store it, I would suggest you have someone start it periodically, drive it out and about a bit operating the PTO and everything else on it. 3 yrs is a LONG time for a piece of equipment with hydraulics and engine to sit around idle----seals will dry out, coolant will deteriorate (break down), moisture will condensate inside the engine, hyd cylinders, rear end, and transmission. If it has any hyd rams, including power steering cylinders, they should be coated with a preservative if it is only a coating of clean grease. If it has a dry clutch, you will want to either have someone operate the clutch pedal periodically or tie the clutch pedal down so the clutch discs don't adhere to the flywheel or intermediate metal discs.
If it sits static for 3 years, the tires are apt to dry rot, water pump seals leak, rams begin to rust and pit, and coolant turn to sludge in the bottom of the radiator and engine.
my 2 cents.
Edit:
I should have read the new posts before I submitted my 2 cewnts.
Since you are going to be there, your options are different. Get a maintenance battery charger. This is a charger that classic car collectors use just to keep their battery from going dead--a bare minimum trickle current.
Again tho, treat it as above, with exposed hyd cylinder rams coated. Warm days and cool nights will still result in condensation.
Before you begin staorage, change all the lubricants with new fluid. Old fluid, especially engine oil will contain at least a little corrosives due to heat in the combustion cylinders. New filters too.
I assume that your tractor has a poly fuel tank, which minimizes condensation on the tank walls and top, but doesn't alleviate it completely. Use some fuel stabilizer (whatever is appropriate for your area and climate) and routinely, and before the periodic starting, drain any condensate off the bottom of the fuel tank. If your filters have a water drain, do the same for them. If it is going to be started only ocassionally, I would decrease the belt tension on the alternator/water pump a little, Enough so there isn't much lateral pressure on the WP seals. COVER the EXH stack. Even with a rain flap, it will be full of dirt daubers if you don't.
Routinely inspect the electrical system for signs that rodents have been chewing on the wire looms--if ya don't you may go out one day, turn the key and let all the magic smoke out of the electrical components--or worse--start a fire. Drive the tractor under it's own power enough to insure it doesn't sit with the weight of the tractor's axles in the exact same spot in regards to seals and bearings. When you periodically start it, watch it carefully during warmup to make sure corrosion in the cooling system hasn't caused the thermostat to stick closed.
Can't tell ya much about the a/c, but I would expect that after 3 years, the refrigerant will either be low or all leaked out as no compressor seals 100% over that long of a period--I would definitely run the a/c periodically tho, just to keep refrigerant oil circulated on the seals and the "o" rings thru out the system.
Before you put it back to work, if more than 1 yr has elapsed, I would again change all the fluids especially the coolant.
