Did the can get cold, did the metal lines going through the firewall get cold? Despite directions on some cans that say hold it upright I've found that upside down, move it around, shake it, helps. Center outlet air temp on high/recirc on a properly working system should be 45-50 degrees. It does better with the car moving and air is flowing through the condenser. If its nowhere close to 50 and the compressor is clutching or clutched and the system won't take more refrigerant then it could be a restriction in the system.