I bought the most expensive can they had at Autozone because it came with a nice gauge and longer hose that helps reach where Beaver put the service port. It was on sale for about $45. The expensive can came with a link to a YouTube for operator training. In the training it shows how to set the gauge and squeeze the trigger when the compressor is running. The compressor is on the engine and Beaver engineering called for the fill port to be on the front in a nearly hidden, hard to reach location.
The YouTube makes it pretty simple. You only need one gauge. You don't need the full set of two gauges and complicated hose set like Marty has. I borrowed it just in case, but never found out how to to hook it up. With the Autozone can and gauge, you only have one hose and the fitting only fits the right connection.
The first time I tried it, I ignored the part about the compressor running because I was at the front and could not see the back. It helped cool the dash air a little, but it was not great. In fact, I had myself convinced I needed "professional" service.
At Hilton Head, I asked Gerald how to find quality "professional" service where they understood motorhome A/C. His advice was to buy the cheapest can they had at Wal-Mart and service it myself. He also suggested that it would not be unusual if I needed to do it about once a year on a ten year old system.
I bought the bottom shelf can at Wal-Mart for about $12. At Dillard, Keith Cooper stood by the compressor and kept me informed as to when the compressor cycled on so that I knew when to squeeze the trigger. Cell phones work better than shouting over the noise of the engine.
The A/C has been working well ever since Dillard, including the drive north on I-5 yesterday in 85 degree heat.
If your service port is in the front, get help!