M931A2 compressor does not pump?

[ichudov]

I have an M931A2 semi tractor. It starts and drives (used to).

However, today, it started fine but would not build pressure. There was air in the tanks. Maybe 80 PSI. The pressure was below 90 PSI but it would not start pumping. I purposely bled all air out down to 10 PSI, and it still would not build.

Then I disconnected the line from the pressure governor going to the top of the compressor, and still it would not pump air.

What could cause it. I looked at a few 9-2320-272-24-* Tms and did not find much about that. Thanks

 

[doghead]

So, this didn't help?

COMPRESSED AIR SUPPLY

No air pressure (warning buzzer sounding, air pressure not building to

normal operating range as indicated by gauges) . . . . . . . . . . . . . . . . . . . . . . .

Air pressure does not build to normal operating pressure

(above 80 psi (552 kPa)) according to gauges. . .. . . . . . . . . . . . . . . . . . .


Each has a section for diagnosis.

Did you follow them both, and made no progress?

 

[Suprman]

I recently had to rebuild the unloader in one of my trucks. It would build air slowly if you revved it a little. There is an O-ring that had dried out. The rebuild kit is available from Fleetpride it was around 50 bucks. I had to take the compressor off to do it so if you head that route make sure you have the front and rear gaskets. They can be ordered from any Cummins dealer I had a few around I never order just one gasket.
Will

 

[ichudov]

Doghead, thanks. I was looking in the wrong TM. Sorry. I found the right one searching for your quote.

I did start following the procedure. I disconnected the governor line. Then I felt the output air line. It was not exactly hot, but it was warm, on a cool day.

I simply followed the "warm" line by hand. It led me under the truck to a big pneumatic component under the truck, in front of the middle axle. And there, I think, I found the problem: All the air was coming out of the bottom of that component. (note that I photographed it from underneath, so the bottom is the nipple in the middle of it).

Photo of it is attached.

I am going to do some digging and find out what that component is and why it is malfunctioning.

 

[doghead]

You may be able to visually identify that component by looking at TM 9-2320-272-24P-1.

 

[doghead]

Looks like...

 

[Suprman]

If air is coming out of the center of your air dryer or big component as you call it, stick your finger in the hole and push up. Sometimes a little wd40 helps to get it moving again. A rebuild kit is available for that valve.

 

[Triple C]

A person doesn't play with a big truck very long before you get familiar with an air dryer. That by the way is where that air pop off sound comes from when your air gets built up. As Suprman said try some wd40 and I would take off the inlet and spray some in there then start the truck right away and see if that frees it up. Not an uncommon problem and not always a rebuild, sometimes they just stick now and again. Years ago when I drove over the road, one tractor I had drove me nuts with the air dryer, it was rebuilt several times but it just kept sticking. Finally got another one from a wrecked truck and no more problems. They get a personality for sure. Good luck.

 

[doghead]

The picture he posted does not look like the ctis air dryer to me(from looking at the TMs).

 

[Triple C]

You are right doghead it doesn't but it looks just like the one I have on my truck.- BUT, I haven't spent any time under there to make sure that's what it is either!

 

[juanprado]

It is not the ctis dryer but the air brake system electric dryer.

 

[73m819]

It is not the ctis dryer but the air brake system electric dryer.

Could this be used with a 39/809 air system,

 

[juanprado]

I would think so. All it requires is 24v for the heating element, mounting space, and plumbed in . The same model but 12v is used in the hd market.

 

[Triple C]

It is not the ctis dryer but the air brake system electric dryer.

I didn't look at the op's truck, but mine doesn't have the ctis and it looks just like the air dryer I had on my class 8 truck, that's why I assumed that is what it is.

 

[ichudov]

If air is coming out of the center of your air dryer or big component as you call it, stick your finger in the hole and push up. Sometimes a little wd40 helps to get it moving again. A rebuild kit is available for that valve.

Suprman, it was exactly as you said. I came to work today, pushed the valve up with a plastic stick, with a bit of effort it "clicked" and went up a little. Now the air pumps up. In fact, this Holset compressor is amazing in how much air it pumps and how quickly the tanks fill.

This, obviously, is not a complete solution and needs to be properly fixed.

I just bought a rebuild kit for this dryer. Haldex Midland DQ6026 Pure Air Plus Canister Filter Kit .

I think that this stuff is just regular maintenance stuff that needs to be attended to every so often.

Thanks a lot.

 

[Suprman]

I dont believe that kit has the rebuild kit for the expello valve which is whats sticking on yours. It just has the cover piece over the valve. Spray wd40 up into it and see how it goes I think they definetly need some lubricant from time to time. Haldex DQ6020 is the expello valve kit for the ABS air dryer in my 939A2 trucks. It is good to replace the cannister it just unscrews and then you can pick up and out the brown tube piece. You can dump some air dryer alcohol in there with the cannisters out it cant hurt. If you do have to rebuild the expello valve you have to remove the air dryer to do it. I believe there are instructions in the DQ6020 kit.

 

[ichudov]

Suprman, do you think that I need to buy that kit DQ6020, or just spray/lubricate the existing expello valve and call it a victory?

If I was to lubricate it, should I just spray WD-40 from the bottom?

 

[Suprman]

I would try to lube it. Not too much 2 small spurts then build air see if it opens and vents moisture at around 120psi. If you continue to have problems then do the rebuild.

 

[F18hornetM]

Just bought a M931 and it has the same leak at the air dryer as well. The truck is in great shape, almost looks like its been in storage. Think I'll just try some air tool oil in the inlet and see if it will unstick. If that doesn't work will take apart and clean. Let us know how you make out with yours.

 

[F18hornetM]

Found this in case you need it http://www.eriksmilitarysurplus.com/airdrrekitfo.html, says for M35A3, but is same DQ6020 kit part number looks like.