Would repairs to an elevator be classified as a service or construction requirement?
The definition of a service contract is found in FAR part 37, which includes its "primary purpose is to perform an identifiable task". There are examples of services under this definition, the first one being "maintenance, overhaul, repair, servicing, rehabilitation, salvage, modernization, or modification of supplies, systems, or equipment."
A search in the online WD website, now at beta.sam.gov, for elevator repair resulted in WDs under the Service Contract Act. An example of one of the search results is WD #1986-0312 Revision #41 effective 11 Feb 2020 for Arizona.