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Old 06-22-2022, 02:03 PM   #1
Mini-Skoolie
 
Join Date: Jun 2021
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Chassis: Saf-T-Liner
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Saf-T-Liner Air Compressor Issue

Hello,


So today a new issue has arisen. Started my bus (it has been maybe 1.5 to 2 weeks since I started it last) and everything was normal until I started hearing a weird sound coming from under the bus. Didn't think anything of it until I looked at the air gauges in the dash, and since the bus had been running for 15+ minutes, they are normally way past the point that I can disengage the parking brake and move the bus. Instead they were sitting above the red, but not quite high enough to disengage the parking brake, and anytime I pressed on the brake, the gauge would go down and not fill back up.

So I went under the bus to where I heard that weird noise coming from and found air coming out the place circled in red in the first image. I imagine this is the pump for the air compressor, but please correct me if I am wrong. After turning the bus off I could hear air hissing out an unknown place somewhere in the vicinity of where the red arrow is pointing in the second picture. If anyone has any thoughts or has experienced this before, I would love the help.
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Old 06-22-2022, 02:40 PM   #2
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first picture
take a picture of the tag on that unit and post it here and or google it.
your air compressor is mounted to the motor and is either belt driven or hydraulic driven so that is not tour compressor.
second picture is of your proportioning /diverter valve but probably call something fancy.
the arrow is pointing up to some plastic airlines that could be leaking.
get a squirt bottle or pump sprayer with thick soap water in it and spray everything down good while it has some air pressure on it.
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Old 06-22-2022, 02:46 PM   #3
Bus Nut
 
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First pic is your air dryer. Look for a tag on it that identifies the model, I have a spare Bendix AD-IP but it looks like yours is a different model. They can be serviced but it seems to be easiest to replace them unless it's an AD-9.

Get that fixed first and see if things improve drastically.
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Old 06-22-2022, 02:54 PM   #4
Mini-Skoolie
 
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This is the only tag that I see on the unit.
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Old 06-22-2022, 03:07 PM   #5
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bw is bendix brand and the serial number is not working so clean the tape or whatever off so that we can see all of the bottom number.
maybe that is the model.
so far i am seeing bendix AD-IS air dryer module but nothing definite because the PDF isnt wanting to download yet.
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Old 06-22-2022, 03:15 PM   #6
Mini-Skoolie
 
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Are AD-9s hard to replace?
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Old 06-22-2022, 03:30 PM   #7
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Quote:
Originally Posted by Secular_Sam View Post
Are AD-9s hard to replace?
If you can disconnect two air hoses and an electrical connector, you can replace an air dryer. The only reason I didn't do my own is I had to replace the air line to the compressor as well and it was a super tight spot.
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Old 06-22-2022, 03:32 PM   #8
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might be a little tough to rebuild for a newbie but dont look like much to it to replace pay attention and or mark what is connected where.
disconnect it , un bolt it and the install is reverse of take out.
are you sure thats an AD-9?
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Old 06-22-2022, 03:39 PM   #9
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Originally Posted by Jolly Roger bus 223 View Post
might be a little tough to rebuild for a newbie but dont look like much to it to replace pay attention and or mark what is connected where.
disconnect it , un bolt it and the install is reverse of take out.
are you sure thats an AD-9?
I'm pretty sure it's NOT an AD-9, Thomas used weird models that were a little shorter. My bus has an AD-IP, which if I recall is not rebuildable (but probably also cheaper than an AD-9).
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Old 06-22-2022, 03:43 PM   #10
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i just found some ad-9 pictures and its close to the pic and if it is the he can just replace the unloader valve for like 25$ instead of 300$ for a new one.
thats if it is a 9?
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Old 06-22-2022, 03:45 PM   #11
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Quote:
Originally Posted by Jolly Roger bus 223 View Post
i just found some ad-9 pictures and its close to the pic and if it is the he can just replace the unloader valve for like 25$ instead of 300$ for a new one.
thats if it is a 9?
That's a good point - on mine the unloader valve was leaky, but the unit itself had also been "re-sealed" with silicone or something as it was corroding and developing a leak along the seam between the top and bottom half, so I opted to replace the whole thing.
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Old 06-22-2022, 04:04 PM   #12
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Purge valve.. and chances are if the purge valve is sticking / leaking then the cartridge hasnt been change in ages.. that Doesnt like an AD-9.. id just swap with a reman and be done.. be sure to buy one with a heated purge valve if you are up north or plan to drive the bus up north in winter time.. its a MUST.


edited to say doesnt look like AD9
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Old 06-22-2022, 07:57 PM   #13
Mini-Skoolie
 
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Originally Posted by cadillackid View Post
id just swap with a reman and be done.. be sure to buy one with a heated purge valve if you are up north or plan to drive the bus up north in winter time..

Is reman a brand or short for remanufactured?


Thank you all for the help, learning new stuff everyday. I'll update this post once I get it figured out.
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Old 06-23-2022, 06:13 PM   #14
Mini-Skoolie
 
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So the purge valve seemed to be the culprit. Upon replacing it, no more air was coming out except when it need to actually purge.



The first picture is the old valve, I imagine it stopped working because of how gunked up it was around the seals, and the rust on the top.



Second pic is the new one installed.



This third pic is where I am still hearing air come out. Its the red cable just below the electrical plug you see. When I press on the cable in a certain direction the hissing stops and vice versa. So thats a problem I will probably tackle a different day since there are no plans to take this bus anywhere anytime soon.


Random last question, since I have never looked at the purge valve when it purges, liquid (what I am assuming is condensation) can come out of the valve when it purges, correct?
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Old 06-23-2022, 06:41 PM   #15
Bus Nut
 
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Quote:
Originally Posted by Secular_Sam View Post
So the purge valve seemed to be the culprit. Upon replacing it, no more air was coming out except when it need to actually purge.



The first picture is the old valve, I imagine it stopped working because of how gunked up it was around the seals, and the rust on the top.



Second pic is the new one installed.



This third pic is where I am still hearing air come out. Its the red cable just below the electrical plug you see. When I press on the cable in a certain direction the hissing stops and vice versa. So thats a problem I will probably tackle a different day since there are no plans to take this bus anywhere anytime soon.


Random last question, since I have never looked at the purge valve when it purges, liquid (what I am assuming is condensation) can come out of the valve when it purges, correct?
Excellent news! Progress indeed.

That red hose is probably part of the emergency/parking brake system. It correlates to the red needle on your dash air gauge. Canít tell exactly what itís going into be that pic.

Under ideal conditions the red and green needles in your air gauge should read the same value. Does the red one drop faster with the engine off auger letting the air pressure go up to 120?
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Old 06-23-2022, 10:22 PM   #16
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that red air line

A rattle snake rattles to warn before it strikes.

That red air line hissing is a rattle........

william
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Old 06-24-2022, 08:46 AM   #17
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Quote:
Originally Posted by Secular_Sam View Post
So the purge valve seemed to be the culprit. Upon replacing it, no more air was coming out except when it need to actually purge.



The first picture is the old valve, I imagine it stopped working because of how gunked up it was around the seals, and the rust on the top.



Second pic is the new one installed.



This third pic is where I am still hearing air come out. Its the red cable just below the electrical plug you see. When I press on the cable in a certain direction the hissing stops and vice versa. So thats a problem I will probably tackle a different day since there are no plans to take this bus anywhere anytime soon.


Random last question, since I have never looked at the purge valve when it purges, liquid (what I am assuming is condensation) can come out of the valve when it purges, correct?



Yes, the purge valve will often emit condensed water- that's why a heated valve is needed in freezing climates. It may also emit oil vapor if your compressor is tired and passing oil.


The red air line is important. Fix it before moving the bus.

Soapy water and a bright light will help you figure out if its a split air line, or a bad quick-connect air fitting

If it is the air line that's leaking, its a five minute fix:

Push the red ring on the fitting inward while pushing in on the red air line and it will disengage the quick-connect allowing the air line to simply be pulled out. If there is enough length remaining, clean any paint off of the surface and cut just the damaged end off of the air line and reinsert it into the quick connect, pushing firmly to engage. Give it a good tug to prove it is seated properly.
If its the fitting, they are inexpensive. Don't mess with it, replace it.


Also, it looks as though you've identified your air dryer. Replace the cartridge inside it as it is likely to have been neglected for at least as long as the purge valve was.
Good luck with it.
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Old 06-24-2022, 09:03 AM   #18
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Quote:
Originally Posted by Phantom5824 View Post
Yes, the purge valve will often emit condensed water- that's why a heated valve is needed in freezing climates. It may also emit oil vapor if your compressor is tired and passing oil.


The red air line is important. Fix it before moving the bus.

Soapy water and a bright light will help you figure out if its a split air line, or a bad quick-connect air fitting

If it is the air line that's leaking, its a five minute fix:

Push the red ring on the fitting inward while pushing in on the red air line and it will disengage the quick-connect allowing the air line to simply be pulled out. If there is enough length remaining, clean any paint off of the surface and cut just the damaged end off of the air line and reinsert it into the quick connect, pushing firmly to engage. Give it a good tug to prove it is seated properly.
If its the fitting, they are inexpensive. Don't mess with it, replace it.


Also, it looks as though you've identified your air dryer. Replace the cartridge inside it as it is likely to have been neglected for at least as long as the purge valve was.
Good luck with it.
Regarding the air dryer cartridge, I'm not sure these AD-IP and AD-IS modules have replaceable cartridges like the older AD-9s. I have an AD-IP and it is definitely not something you can just open up and service easily.
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Old 06-24-2022, 11:47 AM   #19
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In bus service, the air dryer is maintained yearly with a desiccant change and the purge valve cleaned/rebuilt/resealed. Yours likely hasn't had that which is why it was leaking. That's actually an AD9 dryer, and parts are still available for it. The cartridge in that, especially in a bus, is done on the bench after the dryer assembly is removed. That ring of bolts is undone and the top cover will then be removed revealing the cartridge. The cartridge just spins off with a strap wrench. As I said, these are usually done on the bench because you usually can't get the cover off with it installed, especially in a bus.

The other leak you have, the red line, is a push to connect fitting, and those will often leak because of age. The nylon line will get an indent in it from the fitting's clamp and then leak air. That's why it leaks pushing vs not. Simply remove the line, cut it off after the indent, and then reinstall the line back in the fitting. Use wd40 to help remove/install the line from the fitting. Some brake cleaner sprayed on it to flush out the dirt also helps.

It is an air leak, though, and needs to be fixed before driving the bus, like every other air leak.
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Old 06-24-2022, 12:19 PM   #20
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first take the control line off the purge valve on the bottom and make sure the governor has not failed in the open position. the unloader valve is located in the top of the compressor not in the air drier. follow the guy that knew the correct term
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