Can hear Air Blowing off while driving

[Team Wilhelm]

I have a Cummins 350 on a 08 Forest River Berkshire. While driving it lately on occasion this year down the hwy I will hear inside the coach the air system blowing off from outside. It will blow about 10 times in a row every 5 seconds or so apart. Sounds like if someone was pressing the air brake pedal? The gauges read ok etc and brakes work fine. Anyone got any idea why it would start doing this ? I have 25K on the unit and this is the first time I’ve heard it. I had a second coach following me last week and they could hear it from following behind me. Thanks…Ron

[JimM68]

Ron, that noise is the system blowing the water out of the it's zupposed to do that... but not that often.

First thing would be to drain the air tanks, see how much water is in them.

[racer7]

i have a 2008 expedition with a 325 cummins on a freightliner chassic. same problem 6 to 8 times air escapinf from sounds like left rear of mh. have been to freightliner 2 times. answer can't fix what you can't find,also paid for 2 service calls.

[Jay Pat]

Park on level ground.
Chock the wheels so that the rig cannot roll forwards or backwards.
Build up air pressure.
Wheels chocked. Now, double check.....
Release the brakes.....
Turn engine off.
With foot off brakes, check that the rig does not move forward or backwards.
Get out and listen for air leaks.
Be prepared to go under rig to find leak. Put your hand on the leak to confirm.
If you find it and don't know what it is, tie something around it, spray paint it. Something to mark the leaking component or hose.
If you know how, remove item and get it fixed or drive to a shop and show them.
Can't find the leak or hear it?
Get someone to go in the rig and press the brake pedal all the way to the floor while you listen.

Plan B:
Also, with air built up, turn off engine and watch air gauges. Watch for air pressure drop at the gauges.
No leak?
Press brake pedal all the way and watch air gauge. there will be a drop in pressure and then the drop should stop and hold.
If it keeps dropping, there is a leak in the service brakes.
Someone will have to hold the brake pedal applied, while you go listen outside for an air leak.

After checking everything, apply parking brakes!!!! Don't forget the brakes!!
Hope this helps! Maybe someone will add or clarify.
Pat

[Jay Pat]

If you hear a sudden noise that sounds like air hose blew off the fitting and there is a sudden loss of air down to nothing, that sounds like the air dryer. The air dryer does this when the air compressor stops building up air (the air tanks are full and no need to build up any more pressure). The air dryer does this sudden release to blow out any moisture collecte in that cycle of the air compressor.
If this is happening just simply driving down the road and not applying brakes, there is a problem. Just driving down the road does not use any meaningful amount of air that would cause many cycles.
If this is the problem, someone else will have to jump in to help. This is beyond the knowledge of Pat.

[Skip426]

Air dischage from the area you discribe, once in a while , would be normal. There may be issuse with the air dryer; service, filter change required. Or the problem could be with the air compressor it's self, not un-loading when top pressure is reached. Are the dash air gauges reading there normal pressure ? Have the air tanks been manually drained ? This should be done every 6 months, F//L manual, even with automatic systems.And if your coach is like mine the factory left the manual drain lanyards coiled up on top of the tanks. Took me 1/2 hour with the gen set pulled forward to locate and route them properly. If manually draining the air tank yields more than a small mist of water there is a problem with that auto-air drier that has to be delt with.

[Team Wilhelm]

Thanks all. Your help is appreciated. For the most part the unit has always blowing off some air while driving as it should under normal conditions. While driving and hearing the air blow off quite often on a few occasions recently I do not seem to be losing air as the gauges are at normal. I drain the tanks monthly. If the unit sits a week etc the tanks don’t lose much air. I'm thinking from all your helpful comments that it might be the air dryer. The mtce on the (Haldex Pure Air Plus) it is every 36 months for a filter change. I have not done a filter change yet as my mech (retired diesel mechanic) said due to the low miles and my driving conditions etc it is still ok. He was planning to change it next spring. I think I will change it in short order and then see what conditions still exist. I will follow some of your recommendations and see what the outcome is. Again a thousand thanks for your all your input. …Ron

[Team Wilhelm]

Originally Posted by JimM68

Ron, that noise is the system blowing the water out of the it's zupposed to do that... but not that often.

First thing would be to drain the air tanks, see how much water is in them.

Thanks. Yes I will check them again for drainage. ...Ron

[Team Wilhelm]

Originally Posted by Jay Pat

Park on level ground.
Chock the wheels so that the rig cannot roll forwards or backwards.
Build up air pressure.
Wheels chocked. Now, double check.....
Release the brakes.....
Turn engine off.
With foot off brakes, check that the rig does not move forward or backwards.
Get out and listen for air leaks.
Be prepared to go under rig to find leak. Put your hand on the leak to confirm.
If you find it and don't know what it is, tie something around it, spray paint it. Something to mark the leaking component or hose.
If you know how, remove item and get it fixed or drive to a shop and show them.
Can't find the leak or hear it?
Get someone to go in the rig and press the brake pedal all the way to the floor while you listen.

Plan B:
Also, with air built up, turn off engine and watch air gauges. Watch for air pressure drop at the gauges.
No leak?
Press brake pedal all the way and watch air gauge. there will be a drop in pressure and then the drop should stop and hold.
If it keeps dropping, there is a leak in the service brakes.
Someone will have to hold the brake pedal applied, while you go listen outside for an air leak.

After checking everything, apply parking brakes!!!! Don't forget the brakes!!
Hope this helps! Maybe someone will add or clarify.
Pat

Yes this helps. Many thanks

[Team Wilhelm]

Originally Posted by racer7

i have a 2008 expedition with a 325 cummins on a freightliner chassic. same problem 6 to 8 times air escapinf from sounds like left rear of mh. have been to freightliner 2 times. answer can't fix what you can't find,also paid for 2 service calls.

Yes I also went to dealer and they found nothing and was charged a service call. That's when I learned that I should deal with a mech more so no this issue. Most times a dealer is only smart on the coach itself (if you can be that lucky) and not the frame and chassis. They are super smart till they have your money it seems. ...Ron

[slickest1]

It could be the air governor, but most likely the unloader valves in your compressor. This will cause the compressor to keep pumping air when it should go into bypass mode, causing it to build too much pressure. The pressure has to be released and that is done by the air dryer. You should have a shop look at this problem or it will cost big $. Good luck.

[alf50990]

Team Wilhelm,

What you are describing sounds like short cycling of the air compressor. It is generally due to an issue with the air dryer. The air dryer is one of those out of sight out of mind items that needs to be serviced periodically depending on where you live (humidity levels) and how often you use the coach. You should be able to get info on your specific dryer online or in your manuals. If you are handy you can do the work yourself and save a ton of $$. This happened to us once while traveling so I had to have it fixed on the road and it wasn't cheap. Hope this helps.

Al