Having the units or one unit actually rented out doesn't play into this "per-se".
So long as you are actively trying to rent a unit out, it remains classified as a rental property and depreciation does not stop. Bus should you convert it to personal use, or leave it classified as a rental during your "down time" for renovation and repairs? It depends. Here's a few of my thoughts on the matter.
If you are not attempting to rent it out because the unit is undergoing renovations or repairs, then the unit remains classified as a rental and depreciation continues during the "down time" for renovation and repairs; provided the down time is not extensive. Now the definition of "extensive" is subjective.
If you have a property that is not rented and you are not attempting to rent for an entire calendar year because of ongoing work on the property, then it would probably be best to convert it from a rental to personal use with a conversion date of 1 Jan for the tax year the property will not be rented for that entire 12 month 365 day year. But when you convert it back to rental the following year it's not simple matter of picking up the depreciation where you left off. There's a lot of manual math involved, as the cost basis of the base property will be reduced by the amount of prior depreciation already taken, and the 27.5 year depreciation cycle starts over from year one. Additionally, any property improvements done during the "down time" add to the cost basis.
Also, during the period it's not classified as rental property, standard rental expenses are just flat out not deductible on SCH E. Things like utility costs, property taxes, mortgage interest and property insurance. Only the mortgage interest and property taxes would be deductible as a SCH A itemized deduction, and subject to limits imposed with the TCJA of 2018. Now it's perfectly possible that some of the utility cost could be rolled into the renovation/property improvements costs. You need electricity for running power tools, as well as water for mixing concrete. It's not like those things are free.
