Air compressor governor replacent m923a2

[Kodiakkris400]

The other day while using my 923a2 the pressure relief started blowing off and I noticed the air gauges maxed out. After some research into the air system and logical thinking I did a couple of tests. I removed the unloading line from the compressor and aired up the truck to 120psi only to notice no air coming from the unloading line. I hooked up shop air to the unloader, fanned down the truck to 50psi and fired it up. The truck wouldn't build air as it shouldn't, removed the shop air and it did. I feel it's safe to say the compressor/unloader is functioning properly which lead me straight to the governor. After turning the governor all the way in (lowest pressure possible) the truck airs up to 120psi as normal, then creeps its way to 150 (or past, that's where the gauge stops) and blows the relief. My logical thinking is the governor is malfunctioning, but my main question is I can't find an exact match to the part number on the governor, or a cross reference to another (bendix part#T-293975-D). Anyone have a similar problem and/or used a different replacement part?

 

[Swamp Donkey]

Do your windshield wipers or horn work when it's building too much pressure? If not, I'd look at the PPV before the govenor. If they do, then it's the governor.

 

[98G]

What swamp donkey said. It's almost certainly the PPV.

 

[Kodiakkris400]

The horn and wipers do work

 

[98G]

Then maybe it is the governor. ..

 

[M35A2-AZ]

I would think it is the governor or the line going to it. It is a std. part you can get at a truck parts house.
If the dryer is not popping off, then the compressor is not turning off.

 

[Kodiakkris400]

That's what I was thinking M35A2-AZ. Stopped at Napa in my travels and gave them the part# referenced in the sticky for parts reference at the top of this sub forum. Got a little sticker shock as I've heard alot of people talking $15-$20 for a governor and they quoted me 65+15 for freight as its in Arizona and I'm in Maryland. Suppose I'll be turning back to Google with my new part#. Thanks for confirming my thoughts guys! I hate throwing money at a problem...

 

[juanprado]

Midland kn18530 is the stock unit in most heavy duty apps and will work just fine in the M939. The military uses the higher temp one but it really does not come into play IMHO

 

[M35A2-AZ]

I think the last one I got was around $25-30. and that was at Fleet Pride.

 

[Kodiakkris400]

This may be a trivial question, but the only stupid question is one that isn't asked... Ive looked into the Midland kn18530 and it LOOKS like the same part, but I know looks can be deceiving. The cut in/out specs look the same as the Bendix T-293975-D that's currently in my truck, but the Midland kn18530 lists the Bendix part# it replaces as a 275491. Also just to note I have an M923, not an M939.

 

[painter paul]

It should work fine. Your M923 is one of the M939 series of trucks.

 

[bchauvette]

Last time I got one I went to the Mack dealer. showed them the old governor and asked if they had one. He walked right to the bin. Price was reasonable,
exact match.

Your diagnostics process is spot on, 2 stars

 

[Kodiakkris400]

Thanks again guys! Much appreciated ordered one online to the door for $26 as my work schedule gets hectic and I don't NEED the truck for anything in particular.

 

[Vermonster]

What swamp donkey said. It's almost certainly the PPV.

98G. I know this is an old thread but I wanted to do a little research before I asked yet another dumb question. Ha.
I have the same issue on my Dump Trk. Air builds to 130 or more, relief pops off continuously. It's 25 dgrees up here in the woods . What's a PPV? My horn and wipers Do Not Work with Air Pressure this high. Truck did this once before on a cold morning before my wheel issue, but came out of it. My first thought was the Govenor, but maybe not.

 

[Jbulach]

98G. I know this is an old thread but I wanted to do a little research before I asked yet another dumb question. Ha.
I have the same issue on my Dump Trk. Air builds to 130 or more, relief pops off continuously. It's 25 dgrees up here in the woods . What's a PPV? My horn and wipers Do Not Work with Air Pressure this high. Truck did this once before on a cold morning before my wheel issue, but came out of it. My first thought was the Govenor, but maybe not.

Check the small line that runs from the dryer to the governor for blockage. If blocked look for a coupler in the line a couple feet in front of the dryer, and check for junk or ice in that union if you truck has it.

 

[Vermonster]

Check the small line that runs from the dryer to the governor for blockage. If blocked look for a coupler in the line a couple feet in front of the dryer, and check for junk or ice in that union if you truck has it.

Thanks. I traced the line back up into the frame where it's all tied together in a wad. Didn't see any coupler. Took my small propane torch and "Warmed" the Air Govenor itself, and the fittings around it. Compressor comes on when it should, cuts out at 120, No Relief Valve pop off.
Gotta love Cold Weather.

 

[Mullaney]

Thanks. I traced the line back up into the frame where it's all tied together in a wad. Didn't see any coupler. Took my small propane torch and "Warmed" the Air Govenor itself, and the fittings around it. Compressor comes on when it should, cuts out at 120, No Relief Valve pop off.
Gotta love Cold Weather.

.
Good Deal! Glad you found the solution.

It might be beneficial for you to drain the air tanks when you shut it down for the night... Don't forget to turn the drains back off when you jump back in there to fire it up!