some refrigerants are used simultaneously in automotive, transportation, and residential. Those can be bought with either 608 or 609 certs. If you hold a 609 cert, it allows you to work on automotive and transportation systems like those found in semi refrigerated cargo carriers, so one can say buy R-454 legally with a 609. Many places sell it if you self-certify you hold the proper cert to buy it. But, you are not supposed to work on residential units with just the 609. Both the 608 and 609 can be earned online with inexpensive courses. It has been a while since I looked at the law, but I think that the way it is written, the 609 cert is required to work on a residential unit, or to closely and continuously supervise a registered apprentice who is, with a two year drop dead date for them to acquire their own 608.
HOWEVER, where you will find 3 steps forward and 2 backwards if you get the 608 cert is in the cost to acquire the equipment needed to properly work on a residential HVAC system. What you save in paying others, you will pay double in equipment cost to work with refrigerants. And you will give up space in your tool area for all that equipment. Been there done that. And, every so many years that equipment will become obsolete and you will have to buy it again. However, you will have an excellent understanding of the systems, and that will tell you if someone else knows what they are doing, and if their price quotes are in line.
I've had the 609 cert for eons. Used to do all my own work but stopped when the cost of equipment kept changing to where a savings of $2500 was lost in a cost of $4000 in equipment, which kept changing every 10 years or so. A properly maintained residential HVAC system should not need work beyond cleaning, checking caps, contactors. filters, checking T.E.S.P., etc., over a 10 - 15 year period. Those do not require a license in most jurisdictions for a DIY.
