More than likely, the old condenser was not listed as a physically separate asset. In fact, the entire HVAC system was most likely included in the cost basis of the structure itself, which would be absolutely correct if that old unit was there at the time you purchased or acquired the structure. So you don't "dispose" of it. Just leave well enough alone and continue depreciation of the "ENTIRE" structure "as is". Then add the new condenser as a new asset and start depreciation on it. That new condenser is classified as rental property because the fact is it becomes "a material part of" the structure. So if this is residential rental property it's depreciated over 27.5 years. If it's commercial rental property depreciation is over the next 39 years.
There are those that will argue the condenser is "equipment" and therefore gets depreciated over 5 years. I am not a tax professional by any stretch of the imagination and therefore will not get into the semantics of interpretation of IRS publications. You're going to depreciate the way you want, regardless of what I or anyone else may advise. But if the IRS does an audit for any reason and does not agree with the class identification you chose for the asset, that's between you and the IRS.
One final note - while SEC179 does not apply to rental property assets, you "may" qualify for the 50% special depreciation allowance. In my opinion (and we all know what opinions are like) it's a waste of time to take that special depreciation allowance. Since rental property operates at ever increases losses "on paper" at tax time anyway, taking that allowance will not make one single penny of difference in your overall tax liability. This would only benifit you if your rental property actually produced a taxable profit that was "at least" equal to the 50% special depreciation allowance. I seriously doubt your tax returns shows a taxable profit on line 26 of the SCH E. Though it very well may if you have one or more rental properties for mre than 28 years, or that are paid off and you have no mortgage on it.
