You may not be able to find a service manual but Secretarial Services should be able to get you a owners manual.
Bad news on the AC. Unless you want to pitch a working unit you will have to get used to it. The Armstrong units work great, but tend to be a bit loud. If properly maintained they are hard to kill. I know of no way to quiet them down short of turning it off.
Look at it this way. You will not be disturbud by the campers next to you singing songs late into the night. The AC creates a "white noise" that blocks out other noises quite well.
As to your issues/questions post away, and if possible include pictures. Many here have been down the road you are about to travel and it is much better to lean from someone else than have to figure it all out yourself.