AC's routinely are sold/installed without charging valves.

So, unless your unit has been worked on/serviced in the past it will not have any place to charge with freon.

Note: unless you've developed a 'leak,' it is unlikely that you've lost any freon, and in the event that you have - it will take a Service Tech to install valves and charge your unit correctly.

I would call a Service Tech to assist.

hope this helps.