I just dumped in 3 cans from empty and it worked like a charm. In reality it
should have had just a tad more according to the charge weight it specifies
but 3 can is close enough. If you want to get it just right, use a postage
scale the weigh the fourth can and you can get it spot on, if I lived
somewhere really hot I'd do that but mine works fine for the typical high
70s summer day.
Charging by looking at the sight glass or guages alone works for a system
with a TXV like most older systems used, but the 740 has a fixed orifice so
you'll WAY overcharge it if you fill it until the sight glass doesn't have
bubbles.
