North American Technician Excellence, Inc. (NATE) 
is the leading certification program for technicians in the heating, ventilation, air-conditioning, and refrigeration (HVAC/R) industry and is the only test supported by the entire industry. 

As a provider of training and program sessions, MHCA feels that NATE is one of those valuable resources and has provided a link to their website if you'd like information on their organization.