as a new grad I can relate to your problem as everyone nurses, pcas alike here is at least 10-15 yrs my senior in work experience and age. However as the RN I outrank them, they report to me and I have the authority to issue orders which must be obeyed. OK that's fine on paper and yes in reality they will not want to obey someone who they see as new, an outsider, and young.
Communicate with them, talk to them introduce yourself, eat with them at lunch time, sit with them on breaks. Have a chat with them tell them hey I just wanted to see how things are coming with you. I know i''m new and dont have much experience. You guys have been here long, have that experience, I respect that and i want you to work with me help me get to where you are. You know what to do with difficult pts etc. Compliment them when they are doing good, and uh when they are slacking off well you'll just have to remind them that we're all there to care for patients and xyz need to be done can she do it please.
Know what exactly are they PCAS suppose to be responsible for. check to see if its done, if not go find its responsible owner and kindly ask them to do it. Lead by example, every now, glove up and and then step in and help an overworked pca with a particularly nasty diaper change. He'll no doubt remember you as the nurse that helped him clean up diarreah explosion that splattered the walls. Never ask someone to do something you are not willing to do yourself. Now i'm not saying you helping every hour, but be purposeful about it each day volunteer to help with one task taht you ask them to do you must have done at least 1-2x yourself. I helped with vitals but you know what me helping actually slows them down as i'm slower than them BUT its the throught and gesture that counts. I am not that busy so noticed that pca A is super busy so i step in too.
Smile and say thank you. Well that's so far what I have been doing myself and i think its helping to warm up the staff to me and when i'm super busy I notice they are going above and beyond to make my life easier. Your PCAs are your best back up you want them behind you all the way well next to you too. good luck