I was told about the upside down trick about 4 years ago.  I called a company
who rebuilds the cooling units,  the man said if I do not smell ammonia or
see leaks to turn it up side down and shake it and rattle it around, he said
be rough with it.  He said that over the years when the unit is operating out
of level the ammonia can crystallize in different parts of the coils and by
turning upside down and shaking you loosen up the crystals.

Dan