Be very careful; entering your account and routing numbers. IRS will handle account or routing number errors on split refunds the same as for regular direct deposits and mistakes can result in several different scenarios. For example, if:

• You omit a digit in the account or routing number of an account and the number does not pass IRS' validation check, IRS will send you a paper check for the entire refund;
• You incorrectly enter an account or routing number and your designated financial institution rejects and returns the deposit to IRS, IRS will issue a paper check for that portion of your refund; or
• You incorrectly enter an account or routing number that belongs to someone else and your designated financial institution accepts the deposit, you must work directly with the respective financial institution to recover your funds.

IRS assumes no responsibility for taxpayer error. Please, verify your account and routing numbers with your financial institution and double check the accuracy of the numbers you enter on your return.

Source: www.irs.gov