It's not whether you get a refund or tax due. And the withholding doesn't matter. It's if you have a tax liability on your income. Look at your 1040 line 22 for total tax. So as long as Line 22 is more than $7500 (before applying the credit), you'll get the whole credit back.
The EV credit only reduces the tax liability on 1040 line 22 to zero. Then you will get back all your withholding. But it doesn't reduce any other taxes on line 23.
But technically you could reduce your tax withholding and get more back in your paychecks if the credit will reduce or wipe out the tax on your income (line 22).
