My understanding is there are 2 types of mortgage interest can be deducted.
1. debt used to buy, build, or improve your home.
Definitely deductable up to 1 milliion and is deductable when calculating AMT.
2. loan proceeds not used to buy, build, or improve your home
up to $100K, and not deductable wehn calculating AMT.
I believe your situation si #2.
IRS has a publication regading definition and qualification. You can find from IRS web site.