The federal government offers a rebate of 30% (up to $1500) for A/C units as well as for heating units.
The Energy Star website (address link below) has posted some Q and A which may be helpful for Arizona consumers.
Q: Do I have to replace both my heating and air conditioning to qualify for the tax credit?
A: The law does not require that you replace both your heating and air conditioning, but practically speaking you will probably have to replace both for the air conditioner to qualify.
Q: Is the $1,500 tax credit available for each product?
Can I get $1,500 for windows and another $1,500 for a new HVAC system?
Can I get $1,500 in 2009 and another $1,500 in 2010?
Can two people living in the same home both get the $1,500 credit?
A: Even if you purchase multiple products you can only get a maximum of $1,500 over the 2-year period (2009 & 2010).
Basically you can spend up to $5,000 during this 2 year period on a single or multiple products, and get 30% or $1,500 (30% of $5,000 = $1,500) back as a tax credit.
If you get the entire $1,500 credit in 2009, then you can't get anything additional in 2010.
Click here for the Energy Star Website Q&A and explanations.