D.C. Mun. Regs. tit. 17, r. 17-301
The provisions of this chapter shall be applicable to persons, firms, and corporations engaged or employed in the business of installing, maintaining, repairing, or replacing air conditioning and refrigeration equipment, except as provided in § 302, and subject to the limitations set forth in this section.
A person, firm, or corporation licensed under this chapter to engage or to be employed in the business of installing, maintaining, repairing, and replacing refrigeration or air conditioning equipment shall, in connection with the original installation of equipment, be limited to connecting that equipment to the following:
The ten-foot (10') distance between the equipment and shut-off valve or disconnecting means shall be measured without regard for any intervening object other than a wall or partition.
Each disconnecting means shall be installed under the authority of an approved electrical permit, and each shut-off valve and approved drain shall be installed by (or under the supervision of) a licensed master plumber under the authority of an approved permit.
Connection of the public water supply to refrigeration or air conditioning equipment shall be through an approved check valve or vacuum breaker which shall be (or shall have been) installed by a licensed master plumber under the authority of an approved permit.
A person, firm, or corporation licensed under this chapter to engage in the business of installing, maintaining, repairing, and replacing refrigeration or air conditioning equipment shall, in connection with the maintenance, repair, or replacement of any such equipment, be limited to maintaining, repairing, or replacing the various components of refrigeration or air conditioning systems, including but not limited to, compressors, motors, controls, water regulating valves, and condensers.
The limit of electrical repairs shall be from the disconnect means furnished for each motor location, including the replacement of branch circuit wiring on the load side of the disconnect means.
The limit of plumbing repairs shall be between the approved water shut-off valve supplying the system and the approved sanitary drain with which the system is connected, including the replacement of piping.
If any existing component of any refrigeration or air conditioning system is replaced by a component of larger size or capacity which consumes a larger amount of electricity, requires the enlargement of the branch circuit wiring, requires an increase in the capacity of the disconnect means, or requires any other enlargement or increase in the capacity of any component of the system, all replacement work shall be subject to the limitations established under § 301.2 through § 301.5.
If new equipment is added to an existing system, the work required in connection with the installation of new equipment shall be subject to the limitations set forth in § 301.2 through § 301.5.
If an existing piece of equipment is replaced with new equipment, the work required in connection with the installation of the replacement equipment shall be subject to the limitations set forth in § 301.6 through § 301.8.
D.C. Mun. Regs. tit. 17, r. 17-301