TurboTax support does not have a way to tell why refunds are lower, but I can tell you some reasons why you may be seeing a difference. It could be a state refund that you are seeing rather than the federal or it could be an offset.
Sometimes the IRS makes adjustments or withholds part or all of a refund to cover certain debts. Examples of these debts include:
If you have an offset you will receive a letter within a few days of your refund explaining the difference, or you can contact the Bureau of the Fiscal Service to find out why and how much at 800-304-3107 or TDD 866-297-0517, Monday through Friday 7:30 a.m. to 5 p.m. CST.
Please see below for more information about lower than expected refunds:
TurboTax does not know why your refund was reduced by the IRS. If you used the Refund Processing Service, that fee in addition to your TurboTax fees were deducted. The reduction could have been due to a calculation error or a refund offset to pay a debt such as an outstanding student loan, past due state taxes, or past due child support. In any case, you can expect an explanatory letter from the IRS within the next 30 days or so.