I refer to trying to recharge your AC yourself without having adequate equipment to analyze the system’s condition. The gauge on the kit from Autozone or Pep Boys does not measure both sides of the system. It is very easy to overcharge the system with potential damage. Also, even the low side gauge readings are variable for a given level of charge depending on the condition of the compressor and the expansion valve. The proper way is to pull the refrigerant into a recycling machine where it is weighed and the service technician knows how much — if at all — it fell short and how much to add to bring the level to factory specs. This service should include adding a leak detection dye if none is already present and examining the system under ultraviolet light for the presence of leaks. At Don’s the price of $107.50 plus refrigerant and dye includes a free follow-up inspection, while you wait, in a week or two.
Much worse is using refrigerant with “sealer” added. This substance destroys AC systems and destroys professional service equipment.