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Old 06-22-2021, 08:44 PM   #1
Skoolie
 
Join Date: Jun 2015
Location: Toledo OH
Posts: 103
Year: 2006
Coachwork: Thomas
Chassis: Saf-T-Liner EF
Engine: Cat C7 + Allison MD3060
Air alarm wouldn’t shut off but air pressure was fine…

Related issue that happened the same day as this thread…https://www.skoolie.net/forums/f49/t...rts-36363.html

Once I got the engine running, the air alarm went off. I let the pressure get up to 90 or so, but the alarm stayed on with the dash light. Waited a few more minutes…still going off, pressure holding steady. Mind you this was day two with the bus so I forgot that the pressure should have been 120, not 90…

Made a calculated risk move and decided to start driving. Brakes worked just fine, recovered pressure after a stop, even heard the air dryer purging and compressor cutting out normally, but the alarm was still going off. Pressure never went below 90 the whole way home, I think the max was 110 but I don’t remember for sure.

When I got home, I did notice that I could hear an air leak when the engine was off, coming from the air dryer; I’m already planning to replace it. I ran the engine the other day but didn’t drive, tested the brakes, pumped them down and revved the engine to build pressure back, didn’t see any issues. So why wouldn’t the air alarm shut off the other day? Did it “know” there was a problem with the air dryer or is it a possible bad sensor?

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Old 06-22-2021, 09:13 PM   #2
Mini-Skoolie
 
Join Date: Apr 2021
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Year: 2009
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Engine: 7.6
Rated Cap: 26 seats
are you sure it was the "air pressure alarm"? and not something else like doors, seatbelt, low oil ?
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Old 06-22-2021, 11:33 PM   #3
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Originally Posted by slowstepper View Post
are you sure it was the "air pressure alarm"? and not something else like doors, seatbelt, low oil ?
^^^. This is absolutely what I'd look into first. Do you also have a low pressure light? While it's possible that the pressure alarm switch can fail, it's unlikely that your actual air pressure gauge would quit reading accurately...so you most likely *do* have adequate air pressure...which means it's either the sensor or, much more likely, some other alarm. Especially in a new-to-you bus.
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Old 06-23-2021, 12:15 AM   #4
Skoolie
 
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I agree. I had to replace the air dryer on the "new Crown" due to a leak. They can be re-built, but the cost was about a push between re-build/replace so went replace. I still have a small leak towards the back that will get addressed soon. Another thing to check, is your governor. If your pressure is low after addressing the dryer. They aren't difficult or expensive to replace. Your pressure should settle out about 120 psig. A pressure variation down to 100 psig is normal, but down to 90 psig would concern me. If you had a long hill you could use up some of that air. Trust me you don't want to get to lock-up. It happened to me on my previous dump truck (it actually had copper air lines to the chambers and one broke). Fortunately I was on a forest service road (I live off one) and not much traffic. I was able to replace the line and get back to work. One more tip: if replacing the governor, buy a good one, not cheapo. I like Bendix stuff myself.
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Old 06-23-2021, 05:37 AM   #5
Skoolie
 
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I wrote this in a hurry, I forgot to mention that the low air pressure LIGHT was also on in addition to the alarm.
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Old 06-23-2021, 05:51 AM   #6
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Originally Posted by dbsoundman View Post
I wrote this in a hurry, I forgot to mention that the low air pressure LIGHT was also on in addition to the alarm.
Are you sure the light is for low air pressure? I don't know about Thomases but my IC only has a warning beeper and a wig-wag.
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Old 06-23-2021, 05:56 AM   #7
Skoolie
 
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Are you sure the light is for low air pressure? I don't know about Thomases but my IC only has a warning beeper and a wig-wag.
The symbol is a red circle with 3 arrows pointing to the circle. Can’t find a picture of it on google because the search results are dominated by the stupid TPMS symbol.
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Old 06-23-2021, 02:14 PM   #8
Skoolie
 
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Originally Posted by dbsoundman View Post
The symbol is a red circle with 3 arrows pointing to the circle. Can’t find a picture of it on google because the search results are dominated by the stupid TPMS symbol.
Is this what you are looking for? Empty Red Circle
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Old 06-23-2021, 02:16 PM   #9
Skoolie
 
Join Date: Jun 2015
Location: Toledo OH
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Year: 2006
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Chassis: Saf-T-Liner EF
Engine: Cat C7 + Allison MD3060
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Originally Posted by BamaBus View Post
Is this what you are looking for? Empty Red Circle

That is indeed the symbol! So basically, I was getting a low air warning sound/light, but my actual air gauge was registering relatively normal values.


Again, I think my air dryer was leaking the whole time, could it be that the low air sensor was reacting to the air dryer leak?
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