It leaks fast enough that they charged it Thursday, I drove it home Sunday and did have AC to make a less than an hour drive.
How do you test the compressor?
The good news is that the faster it leaks (the bigger the leak) the easier it is to find.
Like Gerald said, you can use a dye or a "sniffer" to find leaks. If the last guy that filled your AC put a dye in, you may already be able to find the leak without adding more refrigerant. Most of the over-the-counter AC charge cans usually contain a dye that is visible to the eye (professional shops generally use the dye that is only visible with ultraviolet light since it is easier to locate small leaks).
On the compressor, look around the pulley (backside where shaft comes out of compressor body (where the seal is located)). Is it oily? Look around the places where one component connects to another (like a hose to compressor or hose to condenser, and where the hose ends metal fittings are crimped on). Signs of oily residue usually indicate a leak. also check the gauge/charging ports (Schrader valves) to see if they are oily (are the dust caps in place?). The schrader valves are the same design as what's in your tires - they can leak or get loose too.
I can't remember ever finding a bad hose (a leak in the rubber part, unless something rubbed through it). Leaks are usually at a point where two components are fitted together, or a cracked weld or pin hole in a condenser or evaporator, or at a seal.
I recall back in the 90's when the shop I worked in was doing a lot of R12 to R134 conversions, we were also changing the rubber hoses too because some of the older hoses would leak R134 "through the rubber" as the 134 molecule is much smaller than R12 (as Gerald mentioned). The new hoses were called "barrier hoses". I don't recall what year your coach is but this should not be an issue for coaches built in 2000+). However if this was happening on your coach it would be a very slow leak (and you would see signs of the leakage on the hose - assuming you can see that section of hose).
Good luck