installed new appliances in a rental house. if i start depreciating this year can I switch the remainder to 179 next year?

[MinhT1]

No. You can only apply the 179 deduction in the year the asset is placed in service.

[AmeliesUncle]

As a side note, Section 179 only applies if the rental rises to the level of a "Trade or Business".  If it does not rise to that level, Section 179 is not allowed (but the Special Depreciation Allowance is still allowed).

[ColeenD3]

You would not be able to switch depreciation methods, you would have to amend the prior years. As AmeliesUncle mentioned, it is not an available option for residential rental property.

Please see another answer from PaulaM.

To qualify for the section 179 deduction, your property must have been acquired for use in your trade or business. 

Property you acquire only for the production of income, such as investment property, rental property (if renting property is not your trade or business), and property that produces royalties, does not qualify. 

But the appliance does qualify for the Special Depreciation Allowance.

See page 17 of IRS Pub 946. You must see 2019 as 2020 version is not yet available.