In order to claim a charitable contribution, you must qualify for Itemized Deductions on your tax return. Chances are you are receiving the standard deduction on your return. If the total tax deductions you enter to not exceed your fixed standard deduction amount, you won't see any changes in your refund.
Please see this link for more information on Itemized vs Standard Deductions: https://ttlc.intuit.com/replies/3302340