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Topic: Air Pressure won't build (Read 3268 times) previous topic - next topic

Air Pressure won't build

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

Re: Air Pressure won't build

Reply #11 –
When was the last time the air dryer was serviced?

Re: Air Pressure won't build

Reply #12 –
Purge valve is open and won't close?

Re: Air Pressure won't build

Reply #13 –
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 –
Quote from: dkeener –
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 –
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 #17 –
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 –
Quote from: dkeener –
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