The credit says I can claim it if I havent completed 4 years of school but since I've been part time I haven't completed 4 years worth of credit hours.
You or someone who claims you as a dependent can only claim the AOC a maximum of 4 tax years regardless of how many calendar years it takes you to get the undergraduate degree. If you or someone who claims you has already claimed it in 4 tax years, you can't claim it a 5th year.
I have only claimed it one year (last year) and according to the PDF it says " first 4 years of postsecondary education (generally, the freshman through senior years of college), as determined by the eligible educational institution." Does this mean I need to ask my school what they define as 4 years?
Four academic years often take more than 4 calendar years. Generally you graduate when you finish your senior year even if it takes more than 4 calendar years. If you haven't finished your senior year, then you would still be eligible for the AOC if you meet the other qualifications.
Most likely. But check out IRS Pub 970 to make sure you meet all the qualifications. It's on page 10, and you need to pay attention to the paragraph that begins "Student Qualifications". https://www.irs.gov/pub/irs-pdf/p970.pdf