It says my son qualifies for 2500 aotc But on final form sg

The credit amount depends on several factors.

The maximum credit is $2,500 per eligible student.  But if your tax obligation goes to zero, you lose some of the credit but you can have up to 40% (or $1,000) refunded to you.  Your modified adjusted gross income needs to be under $90,000 ($180,000 if MFJ).  

Also, if your son received scholarships, this is used in the calculation of the credit for actual expenses paid out.  Make sure you have included all of your expenses in your input to ensure you are getting credits for all expenses directly related to school.  Costs for books directly needed in class can be added to the screen shown below.