Without a market rate of rent, you should be claiming it as a second home. Basically, property that is not rented to make a profit means your expenses are limited to your rental income. If you claimed this as a second home you could deduct mortgage interest and property tax and any PMI mortgage insurance you pay. Since the resident is your son, that would be considered personal use of a second home. You would have to amend your prior year returns to make this change, though. You would lose depreciation and any other repair or maintenance expenses you may have deducted. On the other hand, your income would decline by the amount of rent you reported.
When you sell a second home, the profit is taxable and the loss, is any, is not deductible.
Following are instructions on amending your returns.
https://ttlc.intuit.com/replies/3288565
