R22 is obsolete and reason your hvac technician recommended you to replace whole unit is probably leak on your unit and loss of that refrigerant. Cost of Mo99 is not small + cost of using proper recovery equipement, leak detection and if its possible to seal system overcomes price of new air conditioner. Even if you recover some R22 from your old system, it is not legal to resell it, has to be recycled, also costly!
Every Air Conditioner have nameplate with type and quantity of refrigerant in it.