[rheavn]

My coach is plumbed with mainly 1/4" air lines.  I didn't keep track of how many fittings it took to complete the changeover.  I started by getting the 12V air system air tight as it is kept separate from the main system by a 60 lb check valve.  By starting with that system you will end up checking almost every house system.  But don't stop there.  I then went to the rear six pack in the right side engine compartment and began checking every thing including the six pack, air dryer, etc.  Kept moving forward from the engine to a air system shut off point that is mounted half way toward the front of the coach.  From there I went to the right front basement compartment, where my 110V air compressor is mounted, and worked my way back to the shut off point half way back under the coach.  Still not done!  Inside the coach there are your air gauges, parking brake valve and brake pedal valve.  Once this adventure was over, I was amazed at how many air leaks I had fixed and how seldom my air pump ran.   

Newell changed to 3/8" air lines during the 2000 coach run which caused the air system to respond quicker, but required more volume.  As Newell added more slides, air door and toilets, the 12V air pump could not keep up.  They started taking away air circuits from the 12V system and connecting them to the main air system.  At some point the 12V pump was eliminated and everything was run through the main air system with two 110V air pumps.  Maybe around 2004????

Hope this helps............................