Are tax refunds kept by the IRS if the taxpayer is in an Installment Agreement?

Unfortunately, the IRS will take any refund to which you are otherwise entitled until your delinquent tax is paid in full.  Since you are in the Installment Agreement, I suggest that you revisit your W-4 form and possibly adjust your allowances so that just enough tax is withheld each pay period to pay your income taxes but not overpay (or overpay as little as possible) so that a large refund will not occur.  However, DO NOT claim more exemptions than you are allowed.  That way you will have the use of your money through the year, but you do not want to have a big tax bill next April!