A Universal certification grants you the largest spectrum of HVAC skills. It is required for technicians who service all types of equipment. To become certified, you must pass the EPA Universal Certification exam which will test your knowledge on questions pertaining to all three tiers of certifications.
The third type of HVAC certification is Type III. These technicians focus mostly on servicing low pressure refrigerant. An example of this would be primarily chillers.
If you are looking to service more than what the Type I Certification allows, than consider the Type II certification. Type II certification prepares you to service and maintain larger, industrial sized appliances.
There are different levels of certifications you can get as an HVAC Technician. Type I gives you the training needed to service and maintain small appliances. For example, Type I Certification gives you the ability to service an AC unit.