No sight glass, and a set of gaugse isn't very accurate on a TXV system for this sort of thing, but if you know that the rest of the system is in proper order, you can charge by pressures (high and low, not just low).

Note that a restriction can cause warm left-side vents, as can a low charge, but with a restriction it will appear to have good pressure but still have very low flow.

Running a system with insufficient refrigerant flow will wear out the compressor due to insufficient oil migration.

There are not blend doors in this car, so looking behind the dash is looking the wrong place. However, you say hot air. Hot as in ambient, or hot as in heated? You're down south, so I really can't be sure; ambient is pretty darn hot for you, probably.

Turn the compressor off (EC button), put the controls on LO and measure the temperatures at the left-side and right-side of the center vent. If there's a difference, it's the heater and you have a bad duovalve. If there's no difference, you can completely quit suspecting that anything is wrong with the heater and it is only a cooling problem. Sorry, but I had forgotten this easy test before.