RV Repair: 1997 holiday rambler 32 vacationer, ac unit, harbor freight

Question
on my front roof a/c i lost 120v power supply. i have 120vac at all breakers in electric panel in master bed room.ther is one marked a/c and it also has 120vac but 0vac at unit seems like bad wire. if so how do i pull another wire to unit

Answer
If you have a bad wire, it should have caused the breaker to pop, or could have caused shock if it shorted.  if it just broke and is live up there, you need to worry about an unprotected live wire until you disconnect it.  However, you really don't know for sure if this is the correct wire.  I would buy a cheap signal chaser available at Harbor Freight, that puts a signal on the wire and allows you to follow the signal to the break, or the source of power.  Of course this wire would have to be dead.  I would start at the AC unit since it is dead.  $15 well worth the price to have this tool.  

If you are sure the wire is broken, and you want to run a new on, you can buy raceway at Home Depot that you can attach to the ceiling and it looks decent enough.  Or you can go out the ceiling and run a conduit to the AC along the roof.  you will not be able to pull this wire back and fish another through.  

good luck.  sorry so long with response.  I was camping the last two weeks and forgot to turn off the all experts questions.