Possible air compressor failure M925A2

[Russ Knight]

I think my compressor has failed. My low air alarm activated last night as I was pulling into my driveway. I walked around the vehicle and could not hear any air leaks. Any suggestions of things to troubleshoot? If the compressor is bad, where is the best place to get a 2 stage unit to replace it?

 

[simp5782]

https://www.steelsoldiers.com/showthread.php?t=173377

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[CARMAN]

Not to stick a fork in it but on mine you can hear the air compressor cycle on and off. Its clear as day when mine is running and pumping air.

 

[162tcat]

Tons on info on this. Get to searching. It's unlikely the compressor failed.


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[Russ Knight]

If it turns out to be the compressor, I want to replace it with a two stage one. Anyone have the correct part number and best place to source one?

 

[Tinstar]

Already been covered several times.

Search is your friend.

 

[simp5782]

If it turns out to be the compressor, I want to replace it with a two stage one. Anyone have the correct part number and best place to source one?

Your standard ss296 compressor turns out up to 13.2cu ft of air at 120psi. A very good husky 2 stage only does 14cfm at 90psi. You should not need more air. If you do. Add 10 to 15gal more of tanks and upgrade the main air lines to 3/4". Especially upgrade the glad hand feed lines to 1/2" or 3/4" as they are just 1/4" orginally

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[tobyS]

You seem to be jumping the gun on compressor when the unloader in the head of the compressor is probably stuck. Loosen the tube on the top of the compressor and see if it will build pressure. After you take the unloader tube lose at the top of the compressor, get some air tool oil (Marvel Mystery Oil) in it (it takes a very small funnel) and follow that line to the control on the firewall, then take the control apart, clean and lube it (I use red grease which is near waterproof). Do the easy stuff first, you may be surprised.

 

[porkysplace]

[h=1]TM's for the 939 series trucks[/h]

 

[Russ Knight]

Already been covered several times.

Search is your friend.

I searched first, found virtually nothing that was pertinent.

 

[Russ Knight]

No air coming from the unloader port on top of the compressor.

 

[Russ Knight]

And after further investigation, I’m thinking it shouldn’t. I think the air pressure comes the other direction and that is what controls the unloader which is what cycles the compressor on and off?


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[porkysplace]

TM9-2320-272-24-3.pdf
TM9-2320-272-24-3 Unit, Direct and General support manual for the M939 series truck. 3 of 4. Oct. 1992


TM 9-2320-272-24-3
Section X. COMPRESSED AIR AND BRAKE SYSTEM MAINTENANCE


https://highwayandheavyparts.com/n-10419-brake-air-compressor-troubleshooting-simplified.html

 

[Russ Knight]

When the line is disconnected from the unloader, compressor still won't build pressure.

 

[tobyS]

Sounds like a stuck unloader valve in the head of the pump. It unloads with pressure, so no pressure should make the pump, pump. Some oil may help free it up. It's a pain in the butt to get off to take apart and clean. If you take the output manifold lose you can confirm if the pump is pumping.

With the tube off the pump, use shop air and blow in the other end of that tube and make sure it is open. Watch to see if it blows water and debris.

 

[sandcobra164]

I agree tobyS. I called myself doing some preventative maintenance to my truck by oiling the head of the compressor with PB Blaster through the unloader line. A few drives later and I had the dreaded no air pressure issue. Turns out whatever gunk was available was loosened by the solvent, migrated to the unloader and stuck it. I had to take the head off, clean everything up and it's been fine since. Mine may be different as I'm 250 powered and haven't messed with an A2 variant in many years. Concept of operations is the same though.

 

[Russ Knight]

I removed the line from the unloader and squirted some aerokroil in it. I'll let it sit overnight and see what happens. That back bolt on the unloader looks treacherous.

 

[sandcobra164]

I hope it works but I'm worried you'll be in the same boat soon. Mine was working fine until I sprayed some solvent in the unloader line. After taking the head off and cleaning everything, I feel certain I will be fine for years to come. I was amazed by how much carbon junk was inside the compressor on my truck.

 

[Russ Knight]

I hope it works but I'm worried you'll be in the same boat soon. Mine was working fine until I sprayed some solvent in the unloader line. After taking the head off and cleaning everything, I feel certain I will be fine for years to come. I was amazed by how much carbon junk was inside the compressor on my truck.

Where did you get a gasket set?

 

[simp5782]

Where did you get a gasket set?

A2 gasket/unloader kit napa/haldex 3559545K also found on ebay using that #

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