How should I enter improvement we did in the past year?

Yes, in order to continue to use the depreciation method that you started and accidentally deleted you are on the right track.  (For future reference, HVAC units are considered a component of the house itself and should be depreciated over 27.5 years.  Do not change it on your current year return unless you file a change in accounting method to make the correction.)

Here is a guide for how to go about entering depreciation into TurboTax in order to duplicate the entries that have been made on previous returns to continue the same depreciation.

• Start from the Schedule C or Schedule E section of your return until you get to the Assets/Depreciation section.
• Proceed to the point where you are adding an asset on the page titled Describe This Asset.
• In order to enter the asset exactly as it has been reported in the past, choose the last option on the list, Intangibles, Other Property, then click Continue.
• On the next page titled, Tell Us a Little More, select Other asset type, then click Continue.
• Enter the detailed information about the asset:  description, cost, date purchased or acquired.  Click Continue.
• Move forward with additional details on the next screen, then click Continue.
• Select the appropriate Asset Class, then click Continue.
• Choose the MACRS Convention, then click Continue.
• Select the Depreciation Method, then click  Continue.
• Answer the question regarding Listed Property, then click Continue.  There may be some additional background questions as well, keep going.
• You will eventually come to a screen to confirm the Prior Depreciation, enter the data and click Continue.
• Finally, you will see an Asset Summary screen with the current year depreciation amount listed.  There is also a check-box here to Show Details.  This will open a full description for the asset so you can verify that it matches the previously reported information.  If it does not, you can choose to go Back and re-enter the data that needs to be changed.