My turbo tax refund was showing as $1628 but the amounte refunded by IRS was $444. I left the states in Nov 2018 ands stayed in PA state only. why the refund is less?

There could be many reasons but when the IRS issues a refund smaller than what yiu reported on yiur tax return they always follow up with a letter giving the reasons 2-3 weeks after the refund was issued.   If the letter did not get to you then you should call the IRS to get the reason.  (note that state refunds are issued by the state, not the IRS)