Most require a membership fee for full use of their sites, but there are many pages concerning industry standards that can be accessed for no charge.
Air Conditioning, Heating, & Refrigeration News
Air-Conditioning, Heating, and Refrigeration Institute
Refrigerating Engineers & Technicians Association (RETA)
Refrigeration Articles on the NEWS' Website
Refrigeration Service Engineers Society (RSES)
Indoor Air Quality Association (IAQA)
Mobile Air Climate Systems Association (MACS)
Sheet Metal and Air Conditioning Contractors' National Association (SMACNA)
State Offices- Office of Apprenticeship