Michael - Do you have a link / citation for your 'fifteen percent loss
per year requires repair' statement? It is my understanding that there
is no such EPA requirement for appliances containing less than 50lbs of
CFC/HCFCs.

Travis,

OK, I have what I think is the final answer to these questions, via a
phone conversation with the EPA's head office in Washington: the
information I provided was incorrect, as was its source, an
informational bulletin from one of the major manufactures of
residential central AC systems.

Based on this mornings conversation:

1) As far as the EPA is concerned it's legal for a homeowner to do
any sort of diagnostic or service work on their own AC system, up to an
including instalation of a complete system, provided that they can find
a source willing to sell them the required tools and materials without
their providing proof of holding an EPA 608 certification.

2) There is no limit to the number or frequency of recharges to
comfort cooling system containing less than 50 pounds of refrigerant;
if the homeowner is willing to do so they can recharge as often as they
wish, nor is their any limit to the number or frequency of such
recharges, performed at a homeowner's request by a commercial HVAC
service's EPA 608 certified technician.

According to the EPA these is considerable confusion regarding these
provisions, and these are questions the EPA is frequently asked by HVAC
wholesalers ad other resellers of refrigerant and the equipment
required to charge and service residential AC systems, including large
organizations such as Granger Supply and Home Depot.

I apologize for an inconvenience caused by my incorrect response above,
and can only note that I wasn't making it up "off the top of my
head", I was depending on information from what appeared to be a
reliable source, and according to the EPA representative there is no
EPA document which directly address the issue of homeowner service of
central AC systems