If you still owe money to the IRS, any refund will automatically be held back. However, it will reduce your debt and number of remaining payments. I'm not sure why you would get a refund if your only income is social security though.
If you do have taxable income that requires you to file, you must file, and you should also file for past years if you had income that required you to file. When you don't file a tax return, the IRS creates a substitute tax return in your name in their computer system using your income records (W-2, 1099, etc.). But the substitute return may not be accurate because the IRS does not know about or give you credit for deductions. If you could file and claim a refund for past years, it would also reduce your debt and remaining payments even though you don't get the money directly.
