I had a charitable tax form and it didn't affect my federal refund.

[AnthonyC]

Charitable donations are itemized deductions.  You must be able to itemize your deductions to see any tax benefit from adding these donations.  

This means your total allowable itemized deductions (things like mortgage interest, property taxes, charitable, medical, and job related) must exceed the standard deduction ($6,300 if single or $12,600 if married filing joint) before you see any tax benefits from adding the itemized deductions.

Also, charitable donations are only deductions that reduce the income you pay tax on.  Its possible you could reach a point where between the deductions, exemptions, or credits you have (like child tax credit, education credit), your tax liability has already been reduced to 0.  When you reach this point, any further deductions aren't going to give you a bigger refund.