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Old 05-02-2019, 04:06 PM   #1
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Motorhome won't build air pressure beyond 37lbs

We are getting ready to leave on vacation and my 2006 tiffin allegro bus 42qdp will not build air pressure beyond 37 lbs. I've checked for advice on line and one thought is the air dump valve could be stuck. Another recommendation is to change the air dryer filter. I find it hard to believe that the air dryer filter would be the cause since this issue just arose since Saturday.
The suggestion on the air dump valve is to start the motor and let it run for about 10 minutes and then push the store button multiple times. That sometimes will work. It didn't work.
So the next suggestion is to tap on the air dump valve. The problem is, I don't know where it is. The next suggestion is if that doesn't work, is to remove the air dump valve and spray silicone lubricant in it. Once again I need to know where it is to do that.
We just bought the motorhome in January and this is our first trip in it other than the 400 mile trip home with it. Not real familiar with all the systems on the MH yet so I could really use some help/advice with this. We had hoped to leave for Colorado today when I got off work today. That's not likely, but would like to be on the road by tomorrow.

PS: it is on a Freightliner chassis.

Thanks in advance!
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Old 05-02-2019, 05:01 PM   #2
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You need to listen to the " air dryer " purge valve, sometimes mistakingly called a dump valve.

Its a port on the bottom of the air dryer. It opens to clear any moisture built up while the compressor is pumping. It closes when its time to pump again but can get stuck. Tapping on it may get you going for a while.

Some have threads that you can screw a pipe plug in to see if you build air.
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Old 05-02-2019, 06:18 PM   #3
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Quote:
Originally Posted by twinboat View Post
You need to listen to the " air dryer " purge valve, sometimes mistakingly called a dump valve.

Its a port on the bottom of the air dryer. It opens to clear any moisture built up while the compressor is pumping. It closes when its time to pump again but can get stuck. Tapping on it may get you going for a while.

Some have threads that you can screw a pipe plug in to see if you build air.
You’ll find it on the DS rear near and above the rear axle, usually just above the u joint.
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Old 05-02-2019, 06:58 PM   #4
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Thanks guys! I appreciate the help and will try it first thing in the morning.
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Old 05-02-2019, 09:40 PM   #5
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Same thing happened to me. 2014 Bus 37 ap. Could hear and feel air escaping out of the valve. When the roadside mechanic removed it it broke. Soft brass. He used an extractor to get it out. We found a replacement locally but you could put a 3/8 (I think) pipe plug temporarily.
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Old 05-02-2019, 11:27 PM   #6
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First, make sure your brakes are set, and the wheels are chocked! Then fire up the motor, and go to the back, around the rear wheels, and listen for air leaking, tough with the motor running, I know! Find the air dryer, and reach up and see if air is escaping from the bottom. If it is, shut off your big motor, and get a male to male brass fitting, take the airlines off the side of the air dryer and hook them together using the brass fitting I mentioned. This will bypass the air dryer, and let you go on your trip! You can address the air dryer when you get back home! You can get the brass fitting from any truck parts store, explain what you are doing, and they will know what you need! NAPA will work too!
Not building air past 40 PSI is a pretty major leak, why I think it is your air dryer!
Us truckers all had one of these fittings in our tool box in our semi's, never left home with out one! Rail!
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Old 05-03-2019, 06:30 AM   #7
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Thanks again guys! I appreciate the help! I'm getting ready to go out and follow your instructions. I hope that works. If so I will be carrying a one of those fittings in the future. Probably will anyway. The way things currently are I'm dead in the water.
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Old 05-03-2019, 07:06 AM   #8
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If you choose to replace the valve with a pipe plug, drain your air lines daily until you get a replacement installed. Not a good idea to drive with that plug in if temps are below freezing. I lost a valve on the Alaska highway (in a construction zone, of course) and it took me about 15 minutes to find my plug, remove the valve and replace it with the plug. Drove 100's of miles to Valdez where Tiffin shipped me a new valve.



Also, be sure to pump your brakes repeatedly and pull all drain valves until pressures are removed, before removing the valve.
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Old 05-03-2019, 08:35 AM   #9
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I have had pretty much the same problem, but my leak is on the manual dump valves on the two front air tanks. So far, I have been getting by with occasionally spraying the two offending valves with penetrating oil and exercising them. There is a small wire cable leading from each of the valves to a point just behind the front tires (one on each side) where it ends in a loop you can pull to open the valve to dump any moisture in the system. Took me a long time and lots of crawling underneath to actually find where this intermittent air leak was coming from Maybe this summer I'll replace them.
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Old 05-03-2019, 09:43 AM   #10
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motor home won't build air pressure

(now this is most likely a really dumb question) but advice would be appreciated! We have a gas 2015 32SA, which we really like, but are considering a 2017 Phaeton 36GA, primarily for more power. What is this air pressure problem spoken of? Does it happen in the Phaeton? We have yet to drive one, still in the research phase, we want to be careful to not "step up" and have a lot more mechanical issues. The gasser is pretty simple. Thanks for any advice, my husband is not a very mechanically inclined kind of guy.
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Old 05-03-2019, 06:41 PM   #11
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The diesels are remarkably durable in my opinion. Our current rig has over 101,000 miles (since 2013), and we traded our 2008 Bus at about 75,000 miles. The diesel chassis on these rigs has had very few problems and most of them have been issues I could repair. Things like leaking hydraulic lines, air lines or coolant lines. I've only had 2 shop issues in 100,000 miles. I had an alternator fail this spring (putting out 17+ volts) and a DEF problem coming down from Alaska last year. That issue was from water in a canon plug. I do my own maintenance and periodic service, and find diesels are much less trouble than gas. I've run and repaired both gas and diesel trucks and farm equipment since I was in my teens, and if I had a choice for a vehicle I was going to run hard, forever, it'd be a diesel.
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Old 05-06-2019, 10:02 AM   #12
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We are back up and running as of Friday late afternoon. The bypass around the air dryer worked. I figured our Colorado Springs trip was a bust so I took the Motorhome to a truck repair place and they ended up replacing the air dryer. So we left Sunday for a four night trip to the Amana Colonies, about a 120 mile trip. It's probably a better distance for our first outing anyway.
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Old 05-06-2019, 03:27 PM   #13
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Thanks again for all the advice!
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