Great suggestions, but you really need to go back to the beginning. Only a very few things can cause freezing. Mostly its Air Flow or Refrigerant. Refrigerant is the easiest to check. And by the way, if it's overcharged, it will run hotter not colder. Boyle's Law: Temperature of a gas is relevant to its pressure and the other way around.Also, if it's a split system, you can not weigh in the refrigerant due to varying lengths of the refrigerant lines to the evaporated coils. Simply set the super heat with accurate gauges and temp sensor. We use digital gauges for accuracy. On self contained units, you can weigh in the refrigerant. If this is a Dometic unit with R-410a, it is likely self contained. I find it hard to believe a tech would charge with the wrong refrigerant. If it's R-410, there's a round pink sticker right there on the compressor saying so. Also, the pressures are extremely different for R-410a and other refrigerants. Refrigerants can not be mixed. Superheat is different for different refrigerants. Some of the new refrigerants are blends, but there is a specific PT chart for that refrigerant. If someone mixes them, there is no chart for that mixture.
There are several possibilities for air flow problems:
1. Dirty coils
2. Upgrading the unit BTU capacity without upgrading or having sufficient duct size.
3. Dirty return air filter.
4. Insufficient return air.
If the problem is air flow, one of the above four should correct it.
I would be glad to assist you on the phone
if you still have problems.