Air Pressure won't build

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Air Pressure won't build

January 02, 2023, 04:51:25 pm

Started the coach in the barn where it has been all winter, except for a couple trips around the block, the air pressure built up as usual. Drove the coach over to the house and parked it overnight for use as a porta potty and shower due to plumbing issues in the main house over new years. Started the coach the next day after home plumbing issues resolved and drove it back to the barn, 300 feet.
Got it in the barn but not all the way, so went to check to see how much more to pull in, a tight fit needless to say. By the time I got back in to pull forward the air pressure warning was beeping and the gauges were reading in the 20's. Would jump up to about 40 then drop down to 20. So the air brakes are locked due to low air pressure. Any thoughts how this could have happened overnight? Temps in the mid-60's at night and mid-70's in the day.

Re: Air Pressure won't build

Reply #1 – January 02, 2023, 05:05:15 pm

Could be a major air leak. When you say jump up to 40 lbs. jump do you mean it goes up to
40 lbs. immediately.

Re: Air Pressure won't build

Reply #2 – January 02, 2023, 05:33:28 pm

Locate the D2 air governor back near the engine and give it a couple love taps if no other major air leaks are found.

Re: Air Pressure won't build

Reply #3 – January 02, 2023, 05:41:07 pm

Leaking from one of a dozen places. Your going to have to listen from the back of the bus with engine hatch up. Let some one else raise rpm a bit while you are standing at the rear. That bad of a leak won't require spray soap, you will be able to hear it. Have them release the brakes or you can get it built up enough to release them. You will likely have to listen fast and repeat it. SCOTCH the tires for safety.

Re: Air Pressure won't build

Reply #4 – January 02, 2023, 05:43:43 pm

Building to 40 quickly makes me think d2 is working but if no leak is found then d2.

Re: Air Pressure won't build

Reply #5 – January 02, 2023, 05:45:04 pm

I don't think an air leak as the air bags are staying up, unless there is some kind of backflow valve or they are separate systems. Can't hear any air leak while shut down and no way to hear anything with engine on and in the barn. Will try some love taps on he D2, if I can find it.

Upon engine start the pressure goes to about 20 then jumps to 40 and falls back to 20 almost immediately. Revving engine has no effect, just continues the above cycle.

Re: Air Pressure won't build

Reply #6 – January 02, 2023, 05:48:53 pm

1. As Doug says, possible sticky D2 governor. If percussion doesn't help, you can also try turning the adjusting screw on the top of the governor in and/or out to see if it frees up the internal plunger, as follows:

A. Remove the top cover from the governor.
B. Loosen the adjusting screw locknut.
C. To raise the pressure settings, turn the adjusting screw counter-clockwise. To lower the pressure settings, turn the adjusting screw clockwise. Note: Be careful not to over adjust. Each 1/4 turn of the adjusting screw raises or lowers the pressure setting approximately 4 psi.
D. When proper adjustment is obtained, tighten the adjusting screw locknut and replace the cover.

https://n0c357rmy1njbuit2friqwu.blob.core.windows.net/documents/BrddZ4M0I0EBhB_SD-01-503_US_005.pdf

Re: Air Pressure won't build

Reply #7 – January 02, 2023, 05:51:10 pm

Air bags get air from secondary tank, your leaking from the wet tank supply which supplies air to brakes.

Re: Air Pressure won't build

Reply #8 – January 02, 2023, 05:56:19 pm

There will be a stainless air line running from the d2 to the drier, may be tucked in behind rear frame rail standing facing the engine. That's where I would start.

Re: Air Pressure won't build

Reply #9 – January 02, 2023, 06:04:25 pm

If it's the stainless line you can hear it with the engine running standing near it. If that's it say so and there's a way to patch it to get it in the barn. Getting ahead of ourselves maybe but it's where I would look first. It will leak with the park brakes set or released.

Re: Air Pressure won't build

Reply #10 – January 02, 2023, 06:39:25 pm

The line runs from the compressor to the drier, nor from d2.

Re: Air Pressure won't build

Reply #11 – January 02, 2023, 08:52:57 pm

When was the last time the air dryer was serviced?

Re: Air Pressure won't build

Reply #12 – January 02, 2023, 09:31:08 pm

Purge valve is open and won't close?

Re: Air Pressure won't build

Reply #13 – January 02, 2023, 09:59:39 pm

Have to look at service records for dryer service. Probably 3-4 years I'm guessing. Haven't driven much in that time. Would the dryer stop working that quickly? Will purge valve open by itself?

Re: Air Pressure won't build

Reply #14 – January 02, 2023, 10:12:00 pm

Quote from: dkeener – January 02, 2023, 09:59:39 pm

Have to look at service records for dryer service. Probably 3-4 years I'm guessing. Haven't driven much in that time. Would the dryer stop working that quickly? Will purge valve open by itself?

Dryer cartridge should be changed annually and dryer rebuilt or replaced every 3-4 years. Purge valve is constantly opening and closing as it reaches pressure and then when it drops to build pressure

Re: Air Pressure won't build

Reply #15 – January 02, 2023, 10:15:01 pm

I had my air dryer go a year ago and I couldn't move. Reach under your air dyer with the engine
running and if you have air pouring out of the bottom of the dryer that would be your problem.
I thought about that as soon as I read your post but the air pressure going up and down I through
me as I have never seen that.

Re: Air Pressure won't build

Reply #16 – January 02, 2023, 10:48:57 pm

Quote from: craneman – March 30, 2020, 05:14:57 pm

These are the 2 kits I used, seems complete except for heater.

DQ6020 - Lower Housing Repair Kit - Haldex product

DQ6026 - General Service Kit - Haldex product

Erratic pressure indication can be just the pressure sensor getting old also
https://www.summitracing.com/parts/SWW-82894

Re: Air Pressure won't build

Reply #17 – January 03, 2023, 06:18:28 am

Can I check for air leaks by hooking up my barn air compressor to the coach via the compressor line in the bay with the fuel tank and propane tank? Also won't this give me the pressure needed to release the brakes? When I had the coach towed once the wrecker ran a line from his truck to this connection or was this just for the suspension since he had already pulled the rear axle and the front was lifted off the ground?

Re: Air Pressure won't build

Reply #18 – January 03, 2023, 07:13:55 am

Quote from: dkeener – January 03, 2023, 06:18:28 am

1. Can I check for air leaks by hooking up my barn air compressor to the coach via the compressor line in the bay with the fuel tank and propane tank?
2. won't this give me the pressure needed to release the brakes?

1. Yes
2. same as #1 yes As long as the compressor can keep up with the leak.

Mike

Re: Air Pressure won't build

Reply #19 – January 03, 2023, 09:10:38 am

Quote from: dsd – January 02, 2023, 10:48:57 pm

Erratic pressure indication can be just the pressure sensor getting old also
https://www.summitracing.com/parts/SWW-82894

Don't forget the possibility of a "blue box" failure (since it's a 2002):

Air pressure sending unit where do they ground at?

02 U320 Air gauge stopped working

Intermittent gauges

Re: Air Pressure won't build

Reply #20 – January 03, 2023, 11:13:18 am

Quote from: dkeener – January 03, 2023, 06:18:28 am

Can I check for air leaks by hooking up my barn air compressor to the coach via the compressor line in the bay with the fuel tank and propane tank? Also won't this give me the pressure needed to release the brakes?

On my 2014 when I connected air compressor to the air fitting in my compartment it supplied air to the HWH tanks (2) but did not fill the wet, front or rear tanks.

Re: Air Pressure won't build

Reply #21 – January 03, 2023, 01:22:23 pm

After hearing the symptoms I would have bet money on the steel supply line, or like mentioned possibly the pop off valve under the drier not closing. We all may learn something here. BE SURE and post what the culprit turns out being. Dozens of places for an air leak but not so many leaking that volume of air. Did you listen at the rear of the bus with hatch open and engine running??

Re: Air Pressure won't build

Reply #22 – January 03, 2023, 01:31:50 pm

I'm anxious to find a he culprit as well. However just coming off shoulder surgery so pretty limited in what I can do and maneuverability. I did get the fittings to connect the barn air compressor to the coach to listen for leaks after I love tap the governor.

Has been wonderful hearing all the helpful suggestions so keep them coming.

Re: Air Pressure won't build

Reply #23 – January 03, 2023, 01:42:36 pm

You will be able to hear a leak that big over the noise of the engine. It would have to be huge. My money is on the governor or air dryer preventing air flow. Or the compressor itself.

At this point the low hanging fruit is to just replace the governor. It's easy, cheap, and something worth doing after enough time has gone by anyways.

Re: Air Pressure won't build

Reply #24 – January 03, 2023, 02:32:59 pm

You need some help over there having new shoulder surgery. Don't need to be doing this work. Same thing here.

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