Car AC leak Repair
(1) moisture in the system does NOT cause the suction line to frost up on the outside. Quite the opposite. Moisture in the system will freeze at the orifice tube or Tx valve and block the flow of refrigerant. No refrigerant flow, no cooling. But that will let the ice inside the orifice/valve melt, and it will cool again, then freeze again, and repeat forever.
(2) evap cores are actually more common failures since going to the higher pressure R134a instead of R12. The most common failures I have seen are (a) condenser where a rock or road FOD knocks a hole/crack in the condenser; (b) O-ring failure and most any point and (c) compressor failure. All of the non-compressor parts don't move, so the seals inside there are stressed more and fail more frequently.
(3) some vehicles have what is commonly a receiver/dryer that is on the low pressure side. If the R134a connection is on the evap side of that, you can allow liquid refrigerant in (can upside down) with no problem as that is what the accumulator is for, to prevent liquid refrigerant from reaching the compressor. If you are not sure, always keep the can upright if you are running the compressor to introduce refrigerant.
You can get a good A/C repair book at most auto parts stores. They give details about proper suction and high-pressure line pressures. But by far the best choice is to have the refrigerant reclaimed, then evacuate with a good vacuum pump for at least 30 minutes to boil off all moisture, then fill with specified amount. No guesswork.
Note that newer cars use much less freon. I drive a Toyota Tacoma that requires 22oz, just under two 12 oz cans. My wife's previous Honda was something like 16oz. If you overfill you can quickly buy a compressor, as they do NOT like liquid in the suction line, it won't compress, and something has to give. At idle, you might feel a very rough idle and squealing belt. If you turn it on while on the highway, you will likely hear a rattle of death at the very least...