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Topic: Getting pressure high enough to drive? (Read 682 times) previous topic - next topic

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Getting pressure high enough to drive?
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...

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Re: Getting pressure high enough to drive?
Reply #1
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...

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Re: Getting pressure high enough to drive?
Reply #2
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
Assuming the 25 PSI was with the engine running.
Exactly! The engine has to be running.

P

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Re: Getting pressure high enough to drive?
Reply #4
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. ...

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  • Twig
  • [*][*][*][*][*]
Re: Getting pressure high enough to drive?
Reply #5
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
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

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Re: Getting pressure high enough to drive?
Reply #7
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...

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Re: Getting pressure high enough to drive?
Reply #8
If you had chalky air sounds like a bad air drier.

Re: Getting pressure high enough to drive?
Reply #9
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...

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Re: Getting pressure high enough to drive?
Reply #10
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
I would do a search on the forum for air dryer failure and contamination.

Rich

Re: Getting pressure high enough to drive?
Reply #12
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...

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Re: Getting pressure high enough to drive?
Reply #13
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...

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  • jcus
  • [*][*][*][*][*]
Re: Getting pressure high enough to drive?
Reply #14
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
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...

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Re: Getting pressure high enough to drive?
Reply #16
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...


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  • wayne m
  • [*][*][*]
Re: Getting pressure high enough to drive?
Reply #17
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
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...

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Re: Getting pressure high enough to drive?
Reply #19
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...


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Re: Getting pressure high enough to drive?
Reply #20
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...

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Re: Getting pressure high enough to drive?
Reply #21
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...

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