D.C. Mun. Regs. tit. 17, r. 17-300
The provisions of this chapter shall govern the business of installing, maintaining, repairing, and replacing refrigeration and air conditioning equipment, within the limits set forth in § 301, and require the licensing and bonding of certain persons engaged or employed in the refrigeration and air conditioning business.
Persons, firms, and corporations validly licensed in accordance with the requirements of this chapter to perform work falling within the scope of § 301 shall be considered to be validly licensed under the requirements of § 5 of the Act approved June 18, 1898 (D.C. Code § 2-2106 (1981)) relating to the licensing of plumbers, and under the licensing requirements contained in chapter 1 of this title.
All electrical or plumbing work performed under the authority of this chapter shall, to the extent that any permit is required by the Electrical Code of the District of Columbia or the Regulations Governing the Installation of Plumbing and Gas Fitting in the District of Columbia, be performed only under the authority of a permit issued in accordance with the electrical code or plumbing regulations, and such work shall be performed in accordance with all applicable laws and regulations.
D.C. Mun. Regs. tit. 17, r. 17-300