Originally Posted by Tolew45
1) The gauges on the AC cans are not that accurate, but can be used as a rough guide. AC gauge manifold is the more accurate option [...]
Agreed. A manifold gauge set is the only correct way to assess the situation with an A/C system. Both low and high pressures need to be checked (the low pressure may look OK while the high pressure could be completely off).
Fortunately, manifold gauge sets are not very expensive. I'd suggest buying one before randomly refilling the system with cans of freon.