Richard, my understanding is that only licensed refrigeration
technicians can work with R134a, among other refrigerants. Therefore you providing charging
advice to an untrained person is not only illegal, but also irresponsible. This is one of the reasons the fittings are no longer available for over-the-counter purchase
. Instead, you have to show your license
these components. That the refrigerant is available in auto supply stores is because it is used in auto air-conditioning systems, which are a totally different beast than the capillary tube systems in marine refrigeration
which work under high pressure. Maybe the laws of changed, but I wouldn't want to be the person responsible for another's injury do to the procedure being mishandled.