Well, our A8 has 159k miles now, and the freon doesn’t hold any more, every year @ summer time, we have to take it to the shop to get freon charge and each time it’s $70.00. Now we do it at home for $4.00.
The only way that you can charge Freon to any car is from the LOW port. You can do this with any car, but for the Audis, they covered the low port with some types of sensors. On my A8, the sensor wasn’t there, but the connector is. The location is next to the brake master cylinder and in front of the auxiliary fuse/relay box. Audipages.com will have the pictures.
For Audi A8, you need the adapter like this FJC6016
You can google to find some places that are cheaper with 12 oz freon cans.
The best thing is this device fits perfectly to the threads of the connector and all you need is to connect the can + hose like this.
Turn on the engine, turn on the a/c max, screw the pin of the freon connector hose all the way in to punch a hole in the can, unscrew it slowly until it’s totally out for the freon to get out and flow through the hose. You can feel the can getting very cold, leave it for a while, shake it a few times for the freon to get out completely. When the can is empty, feels lighter and the can doesn’t get cold any more, that’s when the freon is totally out. Turn off the engine, remove the connector, you should be able to feel the a/c inside the car, very cold because the A8 AC is very good.