I made 22,000 this year, i am claiming one child,but i owe4,000 to child support

That depends on how much your spouse made. If your spouse doesn't work and the bulk of your tax refund is from refundable credits, all of it may still be offset because it's attributable to your income.

The IRS doesn't release their formula for calculating Injured Spouse allocations. Most tax preparers believe it's related to income, which means each spouse would be allowed some of the refund. It could just as easily be based on roughly-calculated married filing separate returns. In that case, one spouse might get all the refund, especially if the other was self-employed or subject to penalties on retirement distributions.

The IRS also does not guarantee that they will accept the information on the 8379. For instance, if someone tries to claim that the lower-income spouse pays all the bills for the household and all seven dependent children (joking!), the IRS will decide to re-allocate. There is also no appeal mechanism for Injured Spouse.