[Nebster]

Hi all,

Okay, I'm a complete newbie when it comes to air systems.  (These can't be that complicated though, can they?!)  My coach 120V compressor comes on every 5 minutes like clockwork.  The leak(s) is so fast that I can watch the pressure gauge creep down the whole time.  I mean, it's obviously really bad, and I would have thought I would just be able to walk around and hear the culprit based on what I've skimmed on this forum.

But, no luck.  Even in a very quiet place, I've sat all around the coach and listened intently, and I can't hear anything.  I also have no idea how the whole system is set up or how to start isolating.  I can definitely get Newell to help me this winter, but I thought I'd start here.

Additional plot twists:

1)  Sometimes, in the day time when it's sunny and the coach is warm, the leak disappears.  Don't have enough data to tell whether it might be tied to a slide or some other configuration change.  

2)  I don't have a way to get under the coach safely.

3)  I went ahead and ordered one of those ultrasonic Inficons, figuring worst case I'll still find that tool useful one day when I actually know a little about what I'm doing with the air system and want to hunt down more leaks.  Seems like there's at least a chance it should find this giant, gaping hole somewhere, eh?

Thanks all!

Ben

[encantotom]

there are soooo many air fittings, lines, tanks and devices in the system that a bunch of very small leaks can cause a fast one. fittings can leak, airvalves for various things like the dumps or doors or slides for bay fridges or bbqs are culprits.

air leaks can take a lot of time and at 100 plus bucks an hour you can rack up quite a bill.

start at the obvious places where things are exposed and spray with soapy solution. i use 100% kids bubbles that you get at the dollar store for a buck a pint. it has glycerin or something in it that makes nice bubbles with a spray bottle.

the infinicon whisper is nice and i have one too, but it is an acquired skill to use accurately.

as for getting under the coach. this may be redneck, but if you have some 2x10's you can drive the coach up on a few of them to raise it 3 or more inches. then raise it up using the leveling system and then block it with 22 ton jackstands or big blocks of wood. if your are skinny, you can do it without driving it up on things, but by lifting it up and then blocking or putting jackstands underneath. make sure if yo get underneath, you do have it supported somehow. 55k lbs can flatten you pretty quickly and completely. ask the witch in the wizard of oz that the house fell on.

the real thing about airleaks, and electrical problems is to break it into pieces. isolate into small chunks. btw, newell says i believe that if your compressor comes on once every 45min, that is acceptable. mine is down to only a few times in an 8 hour period. but i have spent a ton of time fixing leaks. that said, i still have an front drivers airbag that goes down in a day. i am going to replace the airbag as i we have looked at everything else.

another way that can seep your supply system down is your brakes. the airbrake system is designed so that if there is a leak in the brake air system, it will steal air from the coach supply air system. if your two brake air gauges are going down quickly as well, then there is something in your brakes. or the check valves for each of your two brake tanks are bad.

there is lots of material on the forum about finding, isolating and fixing air leaks.

welcome to the find a leak club.

tom

[Nebster]

Tom, thanks for the tips on all fronts. Agreed that paying someone else to do this in the long run is not going to be feasible. Maybe the first couple hours, though, would be worth it and do some observing/"helping."

The good news is that I have a large supply of kid bubbles since I have, uh, a kid.

I am pretty skinny and can probably fit under the coach even with the air fully dumped, but it is close. I'll try to figure out the jack points and set up some blocks in a field and see what I can see. That would be worth having around for this initial maintenance rush, I think.

[77newell]

There are 3 groups of air users on my 93 coach; the leveling system, the brake system, and all other users. There are ways of identifying which group(s) are leaking.

As Tom said, if a brake gauge needle is dropping at the same rate as the supply gauge then you have a brake system problem.

Underneath the coach just ahead of the drive axle are a couple 1/4 turn valves. One supplies the leveling system, the other supplies all other users. Shut the valves and check the dash "supply" gauge and the gauge at the rear 6-pack for the leveling system. The dash gauge will show the leakage rate for all other users and the 6-pack gauge will show leakage rate for all of the leveling system.

I think the newer coaches also have a lower pressure system that is fed from the "all other users" supply. This low pressure system feeds the toilets and maybe the slide seals. Others on this site will know. Anyway, there should be a shutoff valve on the feed to this system followed by a pressure gauge. Isolating this system and watching the gauge wii show leakage rate.

Finally, there is one more leak source not yet covered, the 120VAC compressor system itself. If your leakage rate with the engine running is much slower than with the 120VAC compressor then some ting in that compressor system is leaking, usually the dryer though not always.

I have now exceeded the limits of my knowledge and will shut down

[Chester Stone]

Ben, everyone has had different experiences with air leaks. In my case the major leaks were found to be the air fittings connected to the air bags. We discovered these leaks when we changed out all of the air bags. Minor leaks were found in the area of the 120 volt compressor and its tank. There are truck and bus service shops that can raise the coach enough to walk under it and this would be a fast way to apply kid's bubble solution and fix the leaks while up in the air. This approach worked well for me and was not too expensive. Now several hours pass between auxiliary compressor runs.

[Nebster]

Okay, thanks to both of you.

I don't see any air dropping on the brake system. I've also had the entire system shut down while aired up for an overnight and I didn't notice any meaningful bag losses the next morning, although that was far from a scientific test. So my guess is that the leaks are elsewhere.

I will follow up here with whatever I discover, although it'll be a while before I can get to tackling this big block of work.

[77newell]

Be aware that there are all sorts of places for leakage on the leveling side of things without the bags dropping. Leaks occurring from, and including, the 6-packs upstream will allow pressure loss and no change in the air bag pressure when the system is shut down.

[77newell]

Ben: you are going through an experience similar to what most of us on this board have gone through. These coaches are very complex but as you become familiar with the logic of the systems and the associated hardware you will be able deal with most problems expeditiously. The questions you are asking are well thought out, lead to useful information, and the folks here are really willing to offer help. That's a nice combo.

Me? I learned my air system by spending hours under the coach tracing lines that run hither and yon (and back again it seemed). One of the things I learned from that was that Newell put together a well thought out system that has a helpful logic to it. As I came to understand that logic my troubleshooting and search for leaks got easier.

From the questions you've asked I'm confident that you will soon be promoted to guru. Yeah, initially there is so much to try to comprehend that it's outright intimidating. This is one of those cases where persistence pays big dividends. You will likely noodle around struggling to understand how this all works, I know I did. Then suddenly, smack upside the head, the lightbulb goes on and you get it. It feels like a wonderful miracle when that happens. Man does it feel good.

[Chester Stone]

There are approximately 11 air tanks under the coach, most of them are a part of the frame. I found a couple of plugs (drains) leaking.

[ccjohnson]

I have had issues with shift module leaking on my HT740 transmission. Had it rebuilt once at Newell and replaced once by S&S. This will be 3rd time when I get a chance to get to it. You can hear air bubbling through transmission fluid when you put your head inside engine bay in a VERY quiet garage. Both previous repairs have taken 120V compressor cycles from once every 10-15 minutes to once every 4 hrs +/-.