D.C. Mun. Regs. tit. 17, r. 17-303
Except as specifically provided otherwise in this section, no person shall engage in or be employed in the business of installing, maintaining, repairing, or replacing refrigeration and air conditioning equipment, within the limits set forth in § 301, without being licensed to do so.
The licensing requirement in § 303.1 shall not be applicable to persons performing refrigeration or air conditioning work under the personal supervision of, and under the authority of a permit issued to, a validly licensed Master Refrigeration and Air Conditioning Mechanic or Master Refrigeration and Air Conditioning Mechanic Limited, who is responsible for the proper performance of the work.
Nothing in this section shall be construed to prohibit performance of electrical work required in connection with the installation, repair, maintenance, or replacement of equipment by or under the supervision of a person holding a valid license authorizing him or her to perform that electrical work.
Nothing in this section shall be construed to prohibit performance of plumbing work required in connection with the installation, repair, maintenance, or replacement of equipment by or under the supervision of a person holding a valid license as a master plumber.
Work to be performed by any person licensed under the authority of this chapter shall be limited to the work permitted to be performed under the specific license issued to that person.
Each person, firm, or corporation proposing to engage in or be employed in the business of installing, maintaining, repairing, or replacing refrigeration and air conditioning equipment shall first secure one of the following licenses:
It is unlawful for any person to engage in the mechanical work of installation, maintenance, repair, or replacement of refrigeration and air conditioning equipment (except persons not covered by this chapter under § 302) unless he or she has first obtained a Journeyman Refrigeration and Air Conditioning Mechanic's license.
A journeyman's license shall be issued at a time determined by the Director on the basis of a qualifying examination and test of skill in the practical details of this trade given under the direction of the Refrigeration and Air Conditioning Licensing Board.
Each class of license listed in § 303.6 shall entitle the holder of a license coming within that class to perform work related to the installation, maintenance, repair, or replacement of refrigeration or air conditioning equipment for a period of one (1) year, as set forth in § 304.
A licensee shall register any change of address of the licensee's place of business or residence with the Director within five (5) days from the date on which the change occurs.
D.C. Mun. Regs. tit. 17, r. 17-303