Air problem with 923

[jd 9760]

Air pressure max's out and I think is releasing the pop off vavle. What am I looking for? I assume the compressor is not kicking out like it should. Where is the sensor for the compressor located? Or is that not the problem? Thanks

 

[patracy]

The regulator is on the firewall. Off the main feed line. Just before the air horn.

 

[jd 9760]

The regulator is on the firewall. Off the main feed line. Just before the air horn.

Thanks for the info. I also noticed to day the air switch for the 6WD isn't shifting. Switch feels funny and acts like there no air to it or through it. Any chance the two problems are related?

 

[wheelspinner]

Yes. If your pressure protection valve is not operating properly, the "accessory" side of your air system will not pressurize. The signal to the governor to unload the compressor is triggered on the accessory side. This is also where items such as wipers, horn and air shift are tapped from. Look there. I know there are threads from the winter when they froze, but they can gunk up too.

 

[jd 9760]

Yes. If your pressure protection valve is not operating properly, the "accessory" side of your air system will not pressurize. The signal to the governor to unload the compressor is triggered on the accessory side. This is also where items such as wipers, horn and air shift are tapped from. Look there. I know there are threads from the winter when they froze, but they can gunk up too.

Thanks alot I think that was the help I needed

 

[pappa smerf]

Have the same problem including horn, wipers and air shift for front wheel drive not working. Safety valve blowing air out.
Did you get your problem fixed? If so, what did you do?

 

[jd 9760]

Have the same problem including horn, wipers and air shift for front wheel drive not working. Safety valve blowing air out.
Did you get your problem fixed? If so, what did you do?

Not yet I pull the air governor off today and took it apart the thing seems clean on the inside and the spring rod seems to move free but I am not getting any flow on the accessory side of the valve. Does anyone know where I can get a new governor or any sugestions on where else to look. I would say it is the governor that is not working but how do i fix it?

 

[jd 9760]

new symptom: I changed out the air governor today. Fairly cheap $12.00 part at Napa so I thought I'll start there. After I install the new governor, still nothing working. I then remove the air lines from the governor but now I'm mad so I forget to bleed the air system first. I'm sitting on atleast 90psi when I pop the lines off and it's not until I have every line off that I realize I didn't bleed the system and I have NO air at the governor. So I figure air is not getting to the governor. I tried tracing the line back to see where it feeds from but it's 90* with about 150% humidity out side and I lost tract of the line so now I'm back on here........any thoughts?????

 

[doghead]

Change the protection valve, it's your problem.

 

[wheelspinner]

Guys I tried to make this as easy as possible. The pressure protection valve MUST see 70 PSI to allow air into the accessory system. If it is stuck, you will not get air on the accessory side. This means no horn, no axle shift and MOST important NO SIGNAL TO THE GOVERNOR. You wasted your time on the governor, change the PPV and the problem will go away.

 

[jd 9760]

Guys I tried to make this as easy as possible. The pressure protection valve MUST see 70 PSI to allow air into the accessory system. If it is stuck, you will not get air on the accessory side. This means no horn, no axle shift and MOST important NO SIGNAL TO THE GOVERNOR. You wasted your time on the governor, change the PPV and the problem will go away.

It wasn't a total waste of time... Now i can say I know how the change the air governor on a M939!!!!!!!!!!!!!! So where is the PPV located on this beast anyways? And where would I find a replacment?

 

[doghead]

But he saved money by buying the cheapest part first.


When it comes to MVs, there is this magical thing called a Technical Manual. If you can read, you can use it to find and fix problems with your MV. There is even a special TM that only has exploded veiws and part numbers.

They are searchable by words(on your computer).

 

[doghead]

Oh, and this website has a search function too. It really works. If you use it and search for protection valve, you can find other threads that include part numbers and pictures.


And many many times, if you find the part number in the TM, then search it on there site, you can pinpoint the information that will help you.

You need to be thorough and summarize your threads to make this system "go around".

 

[jd 9760]

But he saved money by buying the cheapest part first.


When it comes to MVs, there is this magical thing called a Technical Manual. If you can read, you can use it to find and fix problems with your MV. There is even a special TM that only has exploded veiws and part numbers.

They are searchable by words(on your computer).

Yea I've heard of those things and even read a few but unless you wrote the thing or had experience in the military they are a pain in the butt to read and find anything. Somethings can be found in three different tm's and you may have to look in all of them to figure it out. It's a lot simplier to ask especially if someone on here has had the same problem before and can just tell you where to look. Besides if I learned everything from reading a book I would get to talk to new people like you!!!!!!!

 

[doghead]

Good point, I concede.

Hey Pat, why don't you mention about how we both used TMs today. Neither of us knew exactly which one we needed, but we looked and found what we were looking for.

Took some time, and we both learned a bit more than we knew when we woke up.

Soon, we'll be geniuses.

 

[Bolkbich]

You fella's already are geniuses... One guy parts a truck out , then when it snows he cant remember where he left the parts. The other guy didnt figure out that a truck with 2+ft of center clearance would high-center trying to ride over a pile of cars 6 ft high. We're all human, lighten up and tell the poor guy where the valve is.

 

[jd 9760]

Good point, I concede.

Hey Pat, why don't you mention about how we both used TMs today. Neither of us knew exactly which one we needed, but we looked and found what we were looking for.

Took some time, and we both learned a bit more than we knew when we woke up.

Soon, we'll be geniuses.

I don't know that you need to concede! The tm's can be very helpful if you understand how they are suppose to be used and have the time to look through them.
I did the search you mentioned and came up with ZERO help there, just alot of non related stuff, and I can find nothing in the tm's that refers to protection valve, or protective vavle. There is very little on the air system outside of the compressor. I'm sure the info is there somewhere but I don't have hours to search for it

 

[wheelspinner]

Thanks for the info. I also noticed to day the air switch for the 6WD isn't shifting. Switch feels funny and acts like there no air to it or through it. Any chance the two problems are related?

Yes. If your pressure protection valve is not operating properly, the "accessory" side of your air system will not pressurize. The signal to the governor to unload the compressor is triggered on the accessory side. This is also where items such as wipers, horn and air shift are tapped from. Look there. I know there are threads from the winter when they froze, but they can gunk up too.

Thanks alot I think that was the help I needed

new symptom: I changed out the air governor today. Fairly cheap $12.00 part at Napa so I thought I'll start there. After I install the new governor, still nothing working. I then remove the air lines from the governor but now I'm mad so I forget to bleed the air system first. I'm sitting on atleast 90psi when I pop the lines off and it's not until I have every line off that I realize I didn't bleed the system and I have NO air at the governor. So I figure air is not getting to the governor. I tried tracing the line back to see where it feeds from but it's 90* with about 150% humidity out side and I lost tract of the line so now I'm back on here........any thoughts?????

Guys I tried to make this as easy as possible. The pressure protection valve MUST see 70 PSI to allow air into the accessory system. If it is stuck, you will not get air on the accessory side. This means no horn, no axle shift and MOST important NO SIGNAL TO THE GOVERNOR. You wasted your time on the governor, change the PPV and the problem will go away.

You fella's already are geniuses... One guy parts a truck out , then when it snows he cant remember where he left the parts..... We're all human, lighten up and tell the poor guy where the valve is.

What does getting 2 1/2 feet of snow on top of troop seats laying flat in the middle of a 1 1/2 acre yard amongst piles of sawed lumber and all sorts of other stored items have to do with this post? I offered to go out and poke around for them in the snow before I got a machine out there and you didn't want them until the spring so I didn't worry about it.

As far as helping the OP, his quote to my DIRECT help is above. He chose to completely ignore the suggestion and pursue another path which proved to be more and more frustrating and then comes back and asks yet again the same question. You're right I offered no help or suggestion at all. Even mentioned previous threads that could have been easily searched in MUCH less time than it would have taken me to go find photos etc and repost them yet again considering I was really busy at the time but took a minute to steer him back to the right path, But instead he spent hours chasing and performing an unecessary repair. Lighten up? I gave him the exact answer. The frustration starts after giving advice, seeing the hours spent attempting an unecessary repair and then saying there isn't enough time for hours of searching.

Where is the valve? On the wet tank which is right ahead of the air dryer on my truck.

This is not my truck but is a photo of the valve that I pulled from a quick search on the valve.

 

[doghead]

The solution to the problem was posted with in the 30 minutes of the OP's post.

He doesn't have hours to search, yet has hours to change parts randomly.

2 days have past and his problem is not fixed yet, because he changed the least expensive part.

He changed a cheap part instead of reading for free.

It takes less than 20 minutes to read the table of context for every single TM for the 939 series.

A general search for protection valve will yield the results needed to find the picture of it and the part number . A child could probably find it with a little common sense, in about 20 minutes, from the search results.

Sometimes the best help, is not doing someone elses work. At this point, the op will still be helpless when he has another simple issue. He needs to stop fearing the TMs, and get comfortable with them. They contain much more than we can share in the forums.

 

[porkysplace]

I don't know that you need to concede! The tm's can be very helpful if you understand how they are suppose to be used and have the time to look through them.
I did the search you mentioned and came up with ZERO help there, just alot of non related stuff, and I can find nothing in the tm's that refers to protection valve, or protective vavle. There is very little on the air system outside of the compressor. I'm sure the info is there somewhere but I don't have hours to search for it

Since you don't want to take the time to learn to fix the truck ( or as you say don't have time to learn) , You should hire a mechanic and your problem will get fixed . People hear are more than willing to help you learn , but don't expect instant answers without some effort on your part . To own a MV you have 2 choices either hire someone to fix it for you or make time to learn to use the TM's . I bet if you spent the time reading the tm as you have on this thread you could have found the answer.