Getting pressure high enough to drive?

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Getting pressure high enough to drive?

November 26, 2019, 11:30:12 am

Hi there fellow RVers,
I'm trying to get my mother-in-laws 2003 U320 coach to the shop but have run in to some snags getting it off and running.

By the help of this forum, I was able to get the dead batteries recharged and start the coach but have another problem impeding me from departure.

The panel lights"Level System" with a sustained beeping/warning bell are on and the both front and rear tanks remained at 25 psi for more than an hour. Also, the HWH panel remains unlit and the step cover and outside step will not come in.

Any ideas on how to get the tanks up to pressure where I can drive it to the shop?

Thanks,
Michael

Re: Getting pressure high enough to drive?

Reply #1 – November 26, 2019, 11:35:30 am

Assuming the 25 PSI was with the engine running.

That indicates either a massive air leak (should be able to hear it) or a problem with the air compressor, air governor or air dryer.

If you do not hear an air leak from under the coach or from the air dryer (open engine hatch/back), replacing the air governor is an under $25 and easy to do next step.

Re: Getting pressure high enough to drive?

Reply #2 – November 26, 2019, 11:47:17 am

Make sure the drain valve for the wet tank is closed. Most often mounted under coach ahead of rear axle driver side.

Re: Getting pressure high enough to drive?

Reply #3 – November 26, 2019, 11:49:28 am

Quote from: wolfe10 – November 26, 2019, 11:35:30 am

Assuming the 25 PSI was with the engine running.

Exactly! The engine has to be running.

P

Re: Getting pressure high enough to drive?

Reply #4 – November 26, 2019, 11:50:32 am

Quote from: Doug W. – November 26, 2019, 11:47:17 am

Make sure the drain valve for the wet tank is closed. Most often mounted under coach ahead of rear axle driver side.

Yup, any place large volumes of air can escape will keep PSI from building. But, you should hear that size air leak.

Re: Getting pressure high enough to drive?

Reply #5 – November 26, 2019, 03:42:10 pm

Most likely suspect is the air drier. A search for air drier bypass will probably lead you to the bypass kit and you can air up and drive. It is 3 fittings.

Re: Getting pressure high enough to drive?

Reply #6 – November 26, 2019, 04:30:26 pm

Quote from: Twig – November 26, 2019, 03:42:10 pm

A search for air drier bypass will probably lead you to the bypass kit and you can air up and drive. It is 3 fittings.

Air Dryer Bypass Demo

Re: Getting pressure high enough to drive?

Reply #7 – November 26, 2019, 07:23:50 pm

Many thanks for the suggestions! Yes, engine was running. I did shut it off to listen for a leak but hear or locate one, although it was pretty windy outside so I might not have been able to hear it.

Upon Doug's suggestion I checked the drain valve and it was closed. Quickly opened and shut it to find a burst of chalky air.

I'll check the air drier next time I'm up there.

Thanks,
Michael

Re: Getting pressure high enough to drive?

Reply #8 – November 26, 2019, 07:30:43 pm

If you had chalky air sounds like a bad air drier.

Re: Getting pressure high enough to drive?

Reply #9 – November 26, 2019, 07:51:40 pm

Chalk/white powder in the wet tank drain says the air dryer has FAILED. The desiccant has disintegrated and has entered the coach's air system.

And, that fine white powder is likely clogging quite a lot of the air valves in the coach. The longer it is operated, the more components likely to have been effected.

$$$$$.

Neglecting to service the air dryers can be VERY expensive.

Re: Getting pressure high enough to drive?

Reply #10 – November 26, 2019, 08:52:19 pm

Thanks Ron and Brett. I'll consider bypassing the air dryer as recommended by Chuck.

Chuck, thanks for the elaborate air dyer bypass demo!

Michael

Re: Getting pressure high enough to drive?

Reply #11 – November 26, 2019, 11:48:05 pm

I would do a search on the forum for air dryer failure and contamination.

Rich

Re: Getting pressure high enough to drive?

Reply #12 – November 27, 2019, 09:11:55 am

Quote from: Rich Bowman – November 26, 2019, 11:48:05 pm

I would do a search on the forum for air dryer failure and contamination.

Rich

Thanks Rich I'm doing a little homework on that now. This is my mother-in-law's coach and was not expecting to do much work on it myself! Not that I'm particularly shy of it, but it's kind of hard to do coach-specific troubleshooting as I've been driving up from Dallas to Athens. All I really want to do is just get it to the shop for service and maintenance.

My father-in-law who recently passed away took great care of this coach since he bought it from MOT in 2014. He religiously had it serviced it at MOT. I'm hoping the failing air dyer issue hasn't been going on too long as I would suspect either he or MOT would have noticed? That being said, it has been just sitting in storage since March.

I will be up there tomorrow to attempt the bypass in order to get it up for driving. I'll come back and report win or lose. Wish me luck!

Re: Getting pressure high enough to drive?

Reply #13 – November 27, 2019, 09:52:39 am

Quote from: mlawre – November 26, 2019, 07:23:50 pm

Upon Doug's suggestion I checked the drain valve and it was closed. Quickly opened and shut it to find a burst of chalky air.

Michael,

Couple more things you might try to check before you dive into bypassing the air dryer.

There are at least 3 air tanks on a 2003 U320 - probably 4 tanks if it has a slide. You said you checked the wet tank drain valve and it was closed. There are at least 2 more drain valves (front and rear brake tanks) at the front end of the coach. I'm not sure about the exact location of the drain valves on a 2003. One of the owners of a similar year model may jump in with that info. It would be worthwhile to be sure these other drain valves are fully closed.

Also, if you can locate the air dryer and safely reach it with your hand while the engine is running, you could hold your hand under the exhaust valve on the bottom of the dryer and see if you feel air coming out. If it is stuck open, you would probably not be able to hear it leaking over the noise of the engine running, but you might be able to feel the air blowing out the valve. If you do feel air blowing out the bottom exhaust port, it wouldn't hurt to try rapping it with a hammer. Sometimes a little "percussive persuasion" is all it takes to free up a sticky valve. If it doesn't work - nothing lost. To do the bypass procedure you are gonna get very well acquainted with the greasy underside of the dryer.

Let us know what you find.

Re: Getting pressure high enough to drive?

Reply #14 – November 27, 2019, 11:11:59 am

Should be 3 drains in front of drivers side front tire and check second bay behind drivers front tire, that contains your 12 volt compressor for your slide seals.

Re: Getting pressure high enough to drive?

Reply #15 – December 01, 2019, 05:45:13 pm

Hope all had a Happy Thanksgiving holiday.
Not much time for me to do much troubleshooting as the forces of TG were too strong.

Quick Update: I checked the air drier and did not feel any air blowing out of the exhaust port during the run. The 3 drains in front of the driver's front tire and all were closed. Both front and rear tanks were at ~45 psi and held steady for about 30 min of engine run time. Can I rule out the air drier and/or governor based on these observations?

Also, I noticed that the aux compressor in the driver's bay (at least I think it's the aux compressor) was not running even when flipping the Air Tank switch which was lit when in the on position.

Many thanks,
Michael

Re: Getting pressure high enough to drive?

Reply #16 – December 01, 2019, 06:39:03 pm

Quote from: mlawre – December 01, 2019, 05:45:13 pm

Hope all had a Happy Thanksgiving holiday.
Not much time for me to do much troubleshooting as the forces of TG were too strong.

Quick Update: I checked the air drier and did not feel any air blowing out of the exhaust port during the run. The 3 drains in front of the driver's front tire and all were closed. Both front and rear tanks were at ~45 psi and held steady for about 30 min of engine run time. Can I rule out the air drier and/or governor based on these observations?

Also, I noticed that the aux compressor in the driver's bay (at least I think it's the aux compressor) was not running even when flipping the Air Tank switch which was lit when in the on position.
If you are saying the engine running for 30 minutes kept 45 psi while running you still have a bad governor or a major air leak. No air out the dryer seems to eliminate it though.
Many thanks,
Michael

Re: Getting pressure high enough to drive?

Reply #17 – December 01, 2019, 07:00:47 pm

the air governor was mentioned. sometimes a few good taps with a hammer will
bring it back to life for a short period of time. if you cannot detect air leaks, that
is where i would look first.

Re: Getting pressure high enough to drive?

Reply #18 – December 01, 2019, 07:19:34 pm

Replacing the D2 governor is cheap and simple. Getting the air dryer replaced at any heavy duty truck shop will likely solve most of your problems. This kind of work is well within the skill set of most HD mechanics. You can buy a remanufactured unit, get it installed (should be about an hour's time), get a partial refund for the core of the unit, and I bet by then you will have solved a couple of problems (dessicant escaping to contaminate the whole system, and your low pressure problem).

Re: Getting pressure high enough to drive?

Reply #19 – December 01, 2019, 07:51:45 pm

Quote from: Mike_Sandra_Lloyd – December 01, 2019, 07:19:34 pm

Getting the air dryer replaced at any heavy duty truck shop will likely solve most of your problems. This kind of work is well within the skill set of most HD mechanics. You can buy a remanufactured unit, get it installed (should be about an hour's time), get a partial refund for the core of the unit, and I bet by then you will have solved a couple of problems (dessicant escaping to contaminate the whole system, and your low pressure problem).

Replacing the air dryer is also fairly easy DIY, as long as you have the wrenches. You'd likely have to order from NAPA, DA33100X, IIRC for a Haldex-reman'd unit. You'll need to reuse connectors on the current air dryer and it helps to have someone help hold things.

The tough thing might be the contamination through the system from a failed air dryer. That desiccant gets everywhere in the system when the dryer fails. MOT is familiar with cleaning up the system, likely better than using a truck mechanic for that work.

Desiccant in air system

2003 U320 - Phase 2 of Desiccant Powder Cleanup Complete

Air Dryer desiccant contamination creates symptoms of air leak (split from...

Another Haldex air dryer failure

Desiccant powder in air system - anybody else with this experience?

Re: Getting pressure high enough to drive?

Reply #20 – December 01, 2019, 10:08:56 pm

Figure out how to add air into the system. This will tell if you have air to leak . Meaning that if the comprssor is not working , you wont build air .
It will tell if you have a leak in the system or lack air pressure at the engine/dryer system .

Re: Getting pressure high enough to drive?

Reply #21 – December 02, 2019, 12:18:17 am

Thanks all for the replies!

Ok, based on suggestions I will start with the governor and then try bypassing/replacing the air dryer to see if I can get some pressure built up enough to drive.

Yikes, Michelle! Those links about white desiccant are quite intimidating! I'm not sure I have the savvy to diagnose airlines and check valves. Hopefully, I can get the rig up to MOT and have them assess.

Win or lose, I appreciate all your help!

Michael

Re: Getting pressure high enough to drive?

Reply #22 – January 06, 2020, 12:41:32 pm

Greetings Foretravel Owners and Specialists,
Happy New Year!

I finally made some time to get back up to Athens to try to get my mother-in-law's coach going and report an update.

Update: As suggested, I have by-passed the air dyer by closely following the Dryer Bypass Demo and related posts on this forum. Both tanks are now going up to 130 psi. I am very grateful to have had the wealth of information and guidance of members here to have performed this as I wouldn't have had a clue nor attempted this otherwise.

The step cover and outside sliding step are now working. The awnings are also now working. The coach actually raised. So, I think most of the pressure-related problems have self corrected.

However, I still couldn't get the coach to go into gear. The leveling system light remained lit and alarm kept dinging. The travel mode button would flash intermittently when pushed but go off after a few seconds. The parking brake releases but the 'R' and 'F' just flash when attempting to put the coach into gear.

Eric from MOT suggested that I extend the slides 6" and retract them to reset the sensor, so I plan to do that next time I go out. Thought I might post among the tried-and-true veterans forum though before I go as it's a pretty good drive out there with one solution in mind. Any other ideas would be appreciated.

Also, I ran the engine for a good 30 min or so with the bypass. Is there a good way to purge water from the system? Nacogdoches is about 2 hrs away.

Many thanks,
Michael

Re: Getting pressure high enough to drive?

Reply #23 – January 06, 2020, 01:25:46 pm

Best way to remove the water from the air is to hook up a working air drier.

Re: Getting pressure high enough to drive?

Reply #24 – January 06, 2020, 01:26:28 pm

Quote from: mlawre – January 06, 2020, 12:41:32 pm

Greetings Foretravel Owners and Specialists,
Happy New Year!

Update: As suggested, I have by-passed the air dyer
The step cover and outside sliding step are now working. The awnings are also now working. The coach actually raised. So, I think most of the pressure-related problems have self corrected.

However, I still couldn't get the coach to go into gear. The leveling system light remained lit and alarm kept dinging.

Also, I ran the engine for a good 30 min or so with the bypass. Is there a good way to purge water from the system? Nacogdoches is about 2 hrs away.

Many thanks,
Michael

Easy peasey. don't worry about water accumulation in the air tanks for now. At the end of a full day of driving. open the drain valves on at least the wet tank and allow the air pressure to blow out the water. From there you can judge how much of a problem you have with water accumulation.

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