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. The credit can only reduce the tax to zero. If your non-refundable credits reduce your tax to 0 you will get back all the withholding and payments and any Refundable Credits. Unless you owe for something else like self employment tax or the 10% Early Withdrawal Penalty on IRA withdrawals.
And if your tax on line 22 is less than 7,500 and you want to take advantage of the full 7,500 credit you can increase your taxable income (like convert a traditional IRA to a ROTH IRA or sell some stocks with a gain). That will increase the tax on line 16 but even though it won't increase your refund you won't pay tax on the extra income. Then you won't be paying tax on that income in the future. If this confuses you just ignore it.
