FWIW, freon is only a brand name for refrigerant manufactured by DuPont. Other manufacturers call it by other names. As you are probably aware, due to the fact that you have your CFC certification, if you need to add refrigerant, then there is a leak. It would be a good idea to pressurize and leak check the system, repair the leak, and evacuate into a deep vacuum before charging the required amount of refrigerant into the system. This required amount of refrigerant is critical to the proper operation of the system. It can be found on the unit nameplate. These small systems usually have a capillary tube for the metering device, and the proper amount of refrigerant (measured in oz) must be weighed in precisely. Just trying to "top off" will only cause problems.
It only makes sense to do. For one, it would be a waste of time any money to add refrigerant only to have it leak out again, and two, depending on the rate of the leak, could be in in violation of EPA regulations. IIRC, residential appliances can only leak 10% of total system charge per year before it is required to be repaired.
On another note, most small systems like this will not have service fittings installed from the factory. You first would have to strap on a piercing valve to recover the refrigerant, remove the piercing valve because they should only be used for temporary service, and braze in a service valve. Preferably two valves, one on the low side and one on the high side, so that pressure readings can be taken to ascertain proper operation.
John