Peek in the sight glass, but I don't know if you could see anything worthwile if it isn't running.
And a possible new leak is the fill valve. It may have held just fine but when it was opener to fill it it may not have closed.
A quick check for any pressure in the system would be to quickly and lightly poke a valve and listen for any pressure coming out. Remember you will be releasing valuable freon and you may open a ozone hole over your car (close your sunroof) but it is a test that will tell you something, if you're inclined.
5 speed '91 190E 2.6 320,000 mi. (new car, fast, smooth as silk six, couldn't find any more Peugeots)
5 speed '85 Peugeot 505 2.5l Turbo Diesel 266,000 mi. (old car, fast for a diesel, had 2 others)
5 speed '01 Jetta V6 (new wifes car, pretty quick)
5 speed '85 Peugeot 505 2.2l Turbo Gas 197,000 mi. (wifes car, faster, sadly gone just short of 200k )
5 speed '83 Yamaha 750 Maxim 14,000 mi. (fastest)
0 speed 4' x 8' 1800 lb Harbor Freight utility trailer (only as fast as what's pulling it)