The description of the requirement does not appear to be construction as according to the definition in FAR part 2, construction is work done on "buildings, structures, or other real property", which does not apply to A/C units. Construction does not include the manufacture, production, furnishing, construction, alteration, repair, processing, or assembling of vessels, aircraft, or other kinds of personal property.
The definition of a service contract is at FAR 37.101. A service is performing an identifiable task rather than to furnish an end item of supply. The definition of supply is in FAR part 2, which means all property. The A/C unit is considered property (personal). If the requirement is to replace A/C units and install them, then it can be considered a supply buy. A general guideline (not in the FAR) that contracting officers can use is if the estimated costs of the service or supply exceeds more than 50 percent of the requirement, then it can be classified as such. An example would be the A/C unit itself estimated to be 80% of the total government estimate and the service to install it would be 20%, then the service would be incidental to the supply item and the requirement could be classified as a supply buy. Ultimately the contracting officer will have to make the determination of classifying this requirement as to the type of buy.