The autoclaves operate differently than pressure canners. There is an inner container where the items to be sterilized are placed and they never touch the water. And there is an air purge tube going down into the bottom of the inner chamber to purge air. If you tried to pressure can with the autoclave, this purge tube would be underwater and cause water to spurt out of the top.
You might be able to rig it up for pressure canning (the first pressure canner was an autoclave at the MIT biology department) but it's just not set up for it.
Although if the shit SHTF you could use a canner as an autoclave.
Just drop in a large pot and put the things you want to sterilise in the pot.
My Dad had an autoclave in the training room when he was the trainer for the Houston Rockets.
When they went on the road he'd pack all of his sterilized equipment in obviously sterilized packing.
He was going through the airport one trip and they insisted he open the sterilized packets so they could see what was in them when the x rays obviously showed hemostats and the like.
He raised bloody hell with security and they eventually gave in and let him go after a supervisor was called in.