What type of refrigerant for 2000 Subaru Outback?

R134a. There should be a sticker under your hood with that and other important information about your air conditioning system.

If you are thinking about adding refrigerant to see if you can get the system to work, it is not a good idea. You may succeed in getting a leaky system to work for a while or you may damage the compressor beyond repair. Are you feelin' lucky?

Also, R134a is a very powerful greenhouse gas. According to an article on allpar.com, 1400 times as effective at trapping heat as carbon dioxide. Just in case you have a social conscience.