Thanks for the info. Looks like I will have to drain the lines. I suppose it will be OK to operate the unit without any R134 in it until later. Is that correct?
The unit will not operate without refrigerant in it, of course.
It is okay to leave the compressor in place and drive the coach. I believe you said the belt broke from the compressor pulley seizing. If this is the case you can just leave the belt off - as long as that belt does not also turn other things (like the Alternator and/or water pump). I don't recall what engine you have (and I cant look until finish this post).
One of the reasons these AC compressor replacement jobs fail, is that when the system leaks refrigerant "oil" is lost. It is impossible to know how much oil was lost. Most shops doing a quick repair (i.e. replacing a hose or such) will add some oil back into the system during a recharge, but if too much oil is added the system won't cool properly, and if too little oil is added the compressor burns up (in a short time).
The proper way is to drain all the oil out (either remove the compressor, evaporator, condenser, and receiver/drier and drain - or flush everything thoroughly) then add in the correct amount of oil, putting some in each component). Also, note that a replacement compressor will typically come with oil in it - but that doesn't mean the entire system will have the correct amount of oil after the compressor is installed.
The other challenge in doing AC work on these coaches, is that the "universal AC charge guides" don't have a listing for a Beaver (Monaco, etc.) so the shop doesn't know (can't look up) what the correct amount oil is - or the correct amount of refrigerant to add. If there is a decal with this info on the evaporator housing - you're lucky but many times this decal is gone or ineligible due to age. Fortunately the Owners Manual has this info (at least mine does) and although general it is still useful if that decal is gone. Note how much additional (over a typical truck or car AC system) oil is needed due the 80+ feet of AC hose used on these coaches.