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Old 06-30-2014, 10:24 PM   #1
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Low air pressure warning

Well it happened to the middle of an extended "mix-master" interchange south of Chicago my dash warning alarm went off. It took me a bit of scanning gauges to realize that the warning was for low air pressure in both tanks. I was down to 40psi.

All is well now, but I thought I'd post the details to help someone else!

I was able to get it shut down on the side of the road before the parking brake set, but it was close!
I spent about an hour or so on the side of the road, underneath the coach, on the phone with a friend who is a diesel mechanic. We tried troubleshooting, but couldn't figure out what was going on.

I used our Good Sam ERS for the first time, expecting them to send a tow truck. The dispatcher got on the phone with an RV tech, and relayed to me that they wanted me to drive to a parking lot where they could send a roadside tech to repair.

I confirmed with them that I only had 40psi, and wasn't sure if I could drive.

I did some tests with the brakes: stepping on the brakes to pump the air down to 20psi or so, then seeing if it would build back up. It would go back to 40psi, but no higher.

I then found that by revving to 2500rpm, I could get it up to 70psi. Not enough to turn off the warning buzzer, but pretty close to the 75psi minimum! :-)

With that, I shifted into drive, set it to Manual mode by hitting the Mode button, and shifted down to 3rd. The parking brake was hard to push down, but I was able to get it to stay "off" after a couple tries. Got rolling to the closest exit (3.5 miles down the road!), and worked it into an empty parking lot. The parking brake actually "set" on the road before I got turned in, but I was able to hold it down with my hand and get into the parking lot.

The mobile tech came in about 45 minutes, and immediately felt like I needed to replace the governor on the compressor. My gauges had been showing maxed out since we left home...150psi plus. I had intended to get it checked out. But it bit me before I could.

The tech took out he emergency blow-off valve on the dryer, and found that to be stuck open, replaced that. Apparently the 150+pressure had been causing that to hammer itself to death. I had noticed that I wasn't getting the normal blow-off, but rather a staccato blow off that sounded like a train engine. Apparently the emergency valve beat itself to death, and stuck open.

Next we replaced the governor, because it shouldn't be allowing the compressor to build up that much pressure. Once he got it off, and looked at the pressure adjustment under the end cap, he saw that the pressure adjustment screw was all twisted off. We're still not sure how! That piece was a bit of a bear to replace, because the original installer had put Loctite on the gasket!

Once we got the new governor on, we tested it out. The pressure built up fine, but still didn't blow off at the normal 120-130 range. Instead it kept climbing. I shut it down, and we checked the air line that runs from the governor to the air dryer to trigger the air dryer blow off. He blew in one end, while I held my thumb over the other end. Sure enough, hat hose had a hole in it somewhere...probably caused by the excessive pressure.

We ran a new hose, tested it, and this time we got the normal blow off at about 120psi or so.
The tech made sure everything was secured, and then we were wrapped up and on our way.

Sure, I don't like breaking down, but it could have been a lot worse! And now I know a lot more about my air brakes than I did before! :-)

So if you are on the side of the road with low air pressure, see if running high rpm's will build your pressure up. If you can get 60-70psi, you can probably move. Just remember to shift manually so you can keep your rpm at 2500 or so.

Then, when you've replaced parts, be sure to check the hoses to make sure one isn't blown. It would have been easy for the tech to leave right after replacing the governor, without fully testing the system! Glad he hung around to make sure that not only did it build up pressure, but that it dumped it at the high end also!

And finally, if your air pressure is building really high, check it out before you blow something!

Hope that helps someone else.


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Old 07-01-2014, 07:36 AM   #2
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Thank you for sharing your breakdown experience with all the technical details. I gained some good knowledge about the air system from you.

By the way, it sounds like a good experience with Good Sams ERS; was this the first time? I have them but fortunately have not had the need.

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Old 07-01-2014, 10:03 AM   #3
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Yes, thanks for sharing. I had wondered about this myself.
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Old 07-01-2014, 11:01 AM   #4
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What a story! Sounds like you dodged several bullets there.

Back in the day I worked on HD trucks with air brakes, we had one behaving similar to yours. Municipal driver that didn't care the system was maxing out so they drove it till it quit.

The way it quit was a line blew out dumping the system pressure and engaging the parking brakes at roughly 50MPH. Nobody was hurt but after I laid in a water soaked culvert caging the brakes so they could drag the thing out, getting it back to the shop, fixing the hose just to find that the system needed repair for a couple of weeks? His supervisor dressed him down over that one.
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Old 07-01-2014, 05:38 PM   #5
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Hank, Yes, this was the first time I ever had to use Good Sam ERS. They answered promptly, and were efficient about taking down the details of my issue, and then put me on-hold while they contacted an RV tech. They came back on the call after just a few minutes to relay what the tech recommended. (which was to drive to a parking lot and call them back)

Once I got to the parking lot, I called back, and they confirmed my Good Sam ERS number, asked for my location, then dispatched a mobile tech. They gave me a to-the-minute estimated arrival time. They called me right at that time to see if the tech had arrived. In my case, he hadn't, but when Good Sam offered to contact the mobile company, I said to give him another 10 minutes.

So all in all, I was happy with ERS. I'm pretty sure I basically covered my cost on this one call.

The mobile tech told me that it was a good thing ERS had called his company, and not another one in the area, who would have been much more expensive on the hourly rate. Don't know if that was just "friendly" competition, or true, but the tech they dispatched seemed to know what he was doing, and worked hard to make sure the entire problem was corrected.

I'll be renewing my Good Sam ERS next year!
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Old 07-02-2014, 05:23 PM   #6
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Thanks for taking the time to share! Much appreciated!

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Old 07-03-2014, 05:15 AM   #7
Join Date: Apr 2013
Location: North Carolina
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Thanks for sharing your story. I'm not as familiar with the air pressure system as I should be and this information is good to know. I hope I never have this type issue but if I do I feel a lot more confident I can deal with it now.
I've had to call Good Sam ERS twice. Both for tire blow outs and they've been very good. Once in New Brunswick Canada and they responded in a very timely manner and the service both time has been very good and they do a real good job of keeping you informed about timing of the arrival of the repair tech.

Thanks for sharing

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