M923A2 Compressor Noise

Steel Soldiers is supported by:

fpchief

Active member
Steel Soldiers Supporter
773
61
28
Location
Bay Minette, Al.
Builds air just fine. Has a brand new dryer. The compressor gets louder the closer it gets to being released through the dryer. Just dont remember my last one sounding like this. Video shows the noise vanish as soon as air is released. All good or do I have a problem???


Thank you!!!
 

WillWagner

Loose Nut
Super Moderator
Steel Soldiers Supporter
7,511
150
63
Location
Monrovia, Ca.
IIRC, they are timed....leme see if I can find a book.

And, the timing is for the noise, no other reason. It will not harm things, just the noise.
 

162tcat

Member
676
7
18
Location
Washington
Mine sounds exactly the same. I’ve put about 15k on it without issue. It drives me crazy but it works fine and doesn’t seem to be sounding any worse.


Sent from my iPhone using Tapatalk
 

WillWagner

Loose Nut
Super Moderator
Steel Soldiers Supporter
7,511
150
63
Location
Monrovia, Ca.
Can't find THAT manual either! I must have put them all somewhere where they would be safe. They are safe all right, safe from me ever seeing or using them again!

IIRC, TDC the engine and align the mark, it is just a line, on the comp drive gear with the notch in the front housing on the compressor then stab it in. I think the notch is at the 3 o'clock position when looking at the compressor from the drive end
 

WillWagner

Loose Nut
Super Moderator
Steel Soldiers Supporter
7,511
150
63
Location
Monrovia, Ca.
Another thing that can cause noise is the check valve in the wet tank. If you remove the discharge line at the compressor after pressure is built, engine off, the only air that should come out is what is in the line. If the tank pressure comes back out the discharge line, drains the tank, the check valve is no good. Some can be cleaned, some are throw away ones.
 

Elijah95

Active member
Steel Soldiers Supporter
785
162
43
Location
Georgia
Perfectly normal, put over 12k miles on my 8.3 truck like that no problem


Sent from my iPhone using Tapatalk
 

charlesmann

Active member
176
32
28
Location
Temple, Tx
this was, i thought, a concern too, since i don't remember the civi compressors sounding like this. but since its normal, ill leave well enough alone. @fpchief i noticed your fan wasn't turning. did you mod it with an air activated temp switch? as soon as builds enough, my fan kicks on and is spinning all the while the engine is running. is like to change it to a temp switch, to preserve life of the bearings.
 

Elijah95

Active member
Steel Soldiers Supporter
785
162
43
Location
Georgia
this was, i thought, a concern too, since i don't remember the civi compressors sounding like this. but since its normal, ill leave well enough alone. @fpchief i noticed your fan wasn't turning. did you mod it with an air activated temp switch? as soon as builds enough, my fan kicks on and is spinning all the while the engine is running. is like to change it to a temp switch, to preserve life of the bearings.
Your fan clutch is not supposed to come on until it is given air. That’s why a truck with a failed air compressor and caged brakes will overheat at low speed from no flow.

If your clutch engages once warm, your shutterstat is stuck and needs rebuild/replacement. Easy stuff. Search for it here on the forum


Sent from my iPhone using Tapatalk
 

charlesmann

Active member
176
32
28
Location
Temple, Tx
Your fan clutch is not supposed to come on until it is given air. That’s why a truck with a failed air compressor and caged brakes will overheat at low speed from no flow.

If your clutch engages once warm, your shutterstat is stuck and needs rebuild/replacement. Easy stuff. Search for it here on the forum


Sent from my iPhone using Tapatalk
Once I get a few lbs of air, the fan engages and the wipers move, then go back to the stowed position.

I disconnect the airline going to the fan, it slows down and can be stopped by hand.
 

Elijah95

Active member
Steel Soldiers Supporter
785
162
43
Location
Georgia
Your shutter stat in your coolant line is bad, rebuild or replace it


Sent from my iPhone using Tapatalk
 

Elijah95

Active member
Steel Soldiers Supporter
785
162
43
Location
Georgia
im not finding what you are referring to as a shutter stat in the ipc. could it be called something else?
IMG_4945.jpg
Here is a picture of one on a m939a2 series truck with the 8.3 cummins turbocharged engine


Sent from my iPhone using Tapatalk
 

Elijah95

Active member
Steel Soldiers Supporter
785
162
43
Location
Georgia
@charlesmann if you have a non turbo NHC250 in an M939”A0” or M939A1 series truck, it will be located on the passenger side of the engine near the coolant cross over tube connectionAdjustments.jpg


Sent from my iPhone using Tapatalk
 

charlesmann

Active member
176
32
28
Location
Temple, Tx
That is what i thought you were referring to, but called something else in the ipc.
that was also my initial thoughts as to the first place to start troubleshooting.
I did have an overheating (230-240F) issue but serviced the system 2 additional times and this last test run, i think iv got dialed in. It didnt get above 200. Will do some more testing when i get back stateside in a couple weeks.
Ill also yard off the other item associated with the cooling fan, from my parts truck, and see if that fixes it.
 

Elijah95

Active member
Steel Soldiers Supporter
785
162
43
Location
Georgia
@charlesmann

Follow this thread


It would be worth while to fix this ASAP, as every single time you over heat that engine you’re rolling the dice on your head gasket, possibly scoring cylinder walls, and creating extra wear and tear.


Sent from my iPhone using Tapatalk
 

charlesmann

Active member
176
32
28
Location
Temple, Tx
iv got 2 936A2s, 1 donor, 1 running. The ovr temp was bc it was low of coolant after i did a drain and flush. I thought i had it svced but evidently after driving it a few time around the block, i noticed it very warm. It took 2 additional attempts to get it topped off.
Ill ck that thread out, but it seems, from the initial info with the query, he had the opposite issue, fan not engaging/engaged.
but again, ill ck it out in a couple wks when i get off work.
 

Elijah95

Active member
Steel Soldiers Supporter
785
162
43
Location
Georgia
iv got 2 936A2s, 1 donor, 1 running. The ovr temp was bc it was low of coolant after i did a drain and flush. I thought i had it svced but evidently after driving it a few time around the block, i noticed it very warm. It took 2 additional attempts to get it topped off.
Ill ck that thread out, but it seems, from the initial info with the query, he had the opposite issue, fan not engaging/engaged.
but again, ill ck it out in a couple wks when i get off work.
I’ll explain in depth.

When a shutterstat fails, it can fail in (2) different ways:

Scenario A: Truck runs good, may stay cool at highway speeds, but when idling or running low speeds heats up, and begins overheating rapidly, fan DOES NOT COME ON.

Cause:
1) failure of the wax temp probe failing internally (not serviceable!)
2)failure due to water and corrosion in air circuit caused by bad air drier
3)failure due to long periods of sitting, causing O rings inside shutterstat to stick in place
4)failure due to no air supplied, **please check to see if wipers and air horn doesn’t work, if they do NOT then check PPV (pressure protection valve) located under the truck. Plenty of threads cover this
5) coolant levels low or thermostat STUCK. the shutterstat is at the top of the cooling system, therefor if it never gets warm because coolant doesn’t touch it, or the thermostat is stuck closed not allowing warm coolant to exit engine block and touch shutterstat wax thermal bulb


Scenario B: truck runs good, but after truck builds air pressure the fan runs 24/7 with the engine, pulling LOTS of air and robbing valuable horsepower, as well as wearing the fan clutch bearings/belts faster

Cause:
1) Shutterstat wax temp probe failure internally (NOT serviceable!)
2) shutterstat O-Ring failure, O ring may have shrunken allowing air to bypass where it SHOULD NOT.
3) shutterstat held open from trash or debris getting in, holding valve open. Clean, replace O rings, test in boiling pot of water with air hooked to it then figure out where Debris came from upstream
4)shutterstat tension spring rusted/broken causing air to bypass, remove, repair, replace O rings.

The shutterstat isn’t complicated, it’s simply a wax filled thermostat that actuates a valve with O rings to allow air in when the truck is “too hot” and stop air from flowing when the truck is “not too hot”


Standard, Normal operation is as noted:
Truck is started up, temperature is BELOW 195ish degrees and air pressure is LESS THAN 60psi, horn doesn’t work, wipers doesn’t work; after truck builds up MORE THAN 60-90 psi (depending on what your Pressure Protection Valve is set at under the truck, restricting air to Non-essential accessories to save pressure to stop with essential brakes), you’ll notice your wipers may twitch, and then they and the horn become functional. Fan should NOT have came on at any point here.

Then you’re either idling, or driving, working the truck or not working the truck, whenever it somehow reaches 195-210°F (different shutterstats between “A0”, A1, A2 trucks activate at different temperatures) the wax bulb will actuate a Pin against spring pressure, allowing air to finally flow through and reach the fan clutch, therefor locking it in and allowing additional engine cooling capacity to prevent overheating.

A wholesome guide Written By Elijah95 on basic shutterstat operation and diagnostics



Please note the capitalized words are not yelling, it’s to break up the large paragraphs and emphasize.


Sent from my iPhone using Tapatalk
 
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website like our supporting vendors. Their ads help keep Steel Soldiers going. Please consider disabling your ad blockers for the site. Thanks!

I've Disabled AdBlock
No Thanks