My federal tax refund was only partially sent to my bank account. I'm missing one-third of the payment. Why would the payment be split and when should I expect it?

If your refund was adjusted you should get a letter from the IRS to explain the difference. 

Did you check the IRS site yet ?    When you do click on the DETAILS button to see what happened while you wait for the IRS letter.    If you had unemployment on the return let it be known the original refund will come first then the recalculate portion later ...  https://www.irs.gov/refunds