Mass. Gen. Laws ch. 146, § 88

The provisions of sections eighty-one to eighty-six, inclusive, relative to the examining and licensing of refrigeration technicians, contractors or trainees shall not apply to the installation, replacement, maintenance or alteration of any air conditioning or refrigeration systems, including apparatus or equipment, covered under the provisions of this chapter as are found on the premises or property of such industrial plant, public or private utility company, firm, corporation, hospital, school or college, by a person regularly in the employ of such industrial plant, public or private utility company, firm, corporation, hospital, school or college.