Do all Open Access journals charge Article Processing Charges (APC)?

No. 

 Many OA journals do not charge publication fees (APCs). Indeed, 74% of journals listed in the Directory of Open Access Journals, DOAJ , do not charge APCs. 

 The publishing process is not without cost. Gold OA journals that do not charge APCs rely on funding from universities, academies, funders, libraries, etc., to operate. These are subsidised OA journals and constitute the Platinum OA model, in which articles are free both for the author and for the reader.