If the guts were in fact exposed to atmosphere, it is pretty easy to check for moisture in the system. The HVAC supply houses have "the stuff" to do it with. Not free, but not super expensive.
Lotta if's in this one. If it wasn't an expensive purchase and you didn't plan on getting 20 years out of it, probably worth the effort. If it's a r410a unit, the POE oil does absorb a teeny tiny bit of moisture, about a drop per two ounces. If you are planning to have a tech do the work, probably gonna charge a fortune. Purge with nitrogen and vacuum a couple of times, install a liquid line filter dryer (I would also rig in a slight glass with moisture indicator), vacuum again and charge by weight. Lotta leak checking in there too. Basically, charge to pressure with nitrogen and soap bubble check fittings for leaks while waiting to verify the system pressure holds fast.
If the compressor never ran while there could have been water in the system, there's not much chance of acid formation. If you purge the system well and pull deep vacuum, most of the possible moisture will be removed. Filter dryers are rated for drops if water absorbing capacity, so a drop per ounce of refrigerant is a conservative sizing.
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