Deductions & credits

My question is does the energy tax credit apply independently of income or it phases out at certain income level? 
a qualified  HVAC has a maximum credit of $300. the actual credit allowed is limited by a tax lianility computation line 29 of Form 5695
 
form 5695 instructions
Line 22a. Enter the amounts you paid for energy-efficient building property. Energy-efficient building property is any of the following.
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A central air conditioner that achieves the highest efficiency tier that has been established by the CEE as in effect on January 1, 2009.
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Don't enter more than $300 on line 22a