section 179 deduction disallowed

I have several rental properties. They all showed net income this year.

I elected section 179 deduction for new A/C in one property for $4,500.  Line 11 of form 4562 is 0.

 

"11 Business income limitation. Enter the smaller of business income (not less than zero) or line 5."

 

How could this be if the property is showing a net profit? 

Thanks.