Threaded Mode | Linear Mode

Plecc94

My 2020 Cascadia with DD15 is constantly purging air going down the road despite no visible drops to 100 psi on the gauge to even be running the compressor. I checked my trailer tires for leaks as they have the PSI system and they are good. I started spraying around the engine compartment for leaks and this is the only leak I could find on the air dryer. I’m still not confident it’s going to cause the issue.

It just started today and the only thing I’ve done is swapped a fuse F19 so my CB radio and cigarette plugin works, but I think it also powers something to do with the starter. It has 25A on the chart but all I had was a 30A so plugged it in.

Signature620

Does it have an air dryer? That could be on it's way out.

SquareOne

THAT leak can 100% be your issue. The same very minuscule on my Cascadia was causing the same issue. Replaced the fitting and all was good.

Never actually showed on the air gauge because it was not leaking at the tanks. I'm assuming the governor is sensing the small drop in pressure at the line and causing the compressor to start building for a short time (although the tanks are full). Mine was popping the air every few minutes before the repair.

Plecc94

(10-25-2020 )SquareOne Wrote: THAT leak can 100% be your issue. The same very minuscule on my Cascadia was causing the same issue. Replaced the fitting and all was good.

Never actually showed on the air gauge because it was not leaking at the tanks. I'm assuming the governor is sensing the small drop in pressure at the line and causing the compressor to start building for a short time (although the tanks are full). Mine was popping the air every few minutes before the repair.

Do you happen to know the part number for this fitting?

Also, everytime it does purge, it makes this metallic ping noise. Almost like an alert from the dash but when I had the hood open checking for leaks, I heard it was coming from the air dryer area where the leak is pictured.

Rawze

(10-25-2020 )Plecc94 Wrote: ...
Do you happen to know the part number for this fitting?
...

just about any parts house, stealers$it, etc. for trucks has those fittings. All you need to know is the size hose it belongs to and let em look at the pic.

just for reference...
1/4" brake hose elbows like that usually have 1/8" npt threads on the other end.

3/8" brake hose elbows like that usually have 1/4" npt threads on the other end.

1/2" brake hose elbows like that usually have 3/8" npt threads on the other end.

home depot is your friend for brass adapters form one size npt thread to another.

here are the brass ones I use, I like them better than that plastic crap...
https://amzn.to/35vdlbj

scroll down the page and you will find a lot more of those type of fittings.. I order and keep spares laying around because they are notorious for leaking as they age.

You should also invest in the proper tools for working with those fittings too.. best thing i ever did towards this...
https://amzn.to/3dXDGTk

and my amazon page has a ton of other stuff recommended by myself as well as what others on this forum have shown to be worth having. ref: https://www.amazon.com/shop/rawzescollection

Waterloo

I will second Rawze on those quick release pliers, I have the same set, and it is a life saver when working with these quick disconnect fittings. These babies, same link as above... https://amzn.to/35BxY5X
And when was the last time you changed out the air dryer cartridge? If not in the past year, you should do that too.

Brock

Any leak on the pressure or governor lines can cause that, also if your in a area that's dropped below freezing temps, a frozen line will do that, dump some airline antifreeze down.

On the Peterbilts, the air dryer heater element is on the same fuse as accessories like the CB radio for example, not sure about your truck.

DVT873

"is constantly purging air going down the road despite no visible drops to 100 psi on the gauge to even be running the compressor."..............................................................

This is one of my pet peeves ever since dual circuit air brake systems became the law. So first off do not think in terms of air tanks. Instead think of reservoirs. A tank can and is often subdivided into more than one reservoir. On some heavy duty trucks there is one tank subdivided into 3 reservoirs.

Air leaves the compressor and goes to the air dryer if the truck has one. Today virtually every truck has an air dryer. After the air dryer it goes to the supply reservoir aka "wet tank". Air leaves the wet tank through two lines going out through one way air check valves. The air splits with one line going to a "primary tank" and one going to the "secondary tank" Your dash air gauges are hooked to those two tanks.

There IS NO GAUGE in the supply "wet tank" part of the system. There are plenty of leak points there including the air dryer. The air compressor governor line is connected in that part of the system. Usually to the the reservoir tank. Any leaks in that part of the system will make the compressor run or "cycle"

Air loss in this part of the system WILL NOT show up on your dash gauges. But you compressor will be running. Every time the compressor cuts out the air dryer will purge. That you usually hear. Ever hear a truck idling and every few minutes you hear air going "fsssstt" and stopping? It cycling because of an air leak. What you hear is the air dryer purging. If I had a truck of my own I would put in a gauge so I could see the supply side of the system.

Many times the problem is in the air dryer. These can be a PIA to find if the air leaks off quick. All the NAV's will have a male Compucheck fitting in one of the tanks. The reservoir it is in is always the supply or "wet tank" reservoir. It is there so they can be aired quickly at the end of the assy line for the brake check tests.

Hook shop air up there to air up w/o the engine. Also handy if you need to air up to release and cage brakes when the engine won't start.

Quick link to a generic air system set up.

http://3.bp.blogspot.com/-_NLyluAuvww/VT...system.gif

There are better pics out there but this gives an idea. The check valves aren't blindingly obvious but they are there.

HotRod

I know im a little late on this one, but wanted to throw it out there as well. Sometimes the unloader will hang up in the air compressor as well and not completely unload the compressor, so it continues to build air. When this happens the air will continue to leak out of the purge valve on the air dryer, but with the truck running you will not always hear it. Most guys build up air pressure, then shut the truck off and go look for air leaks. by that time the slight residual air has leaked out the purger valve on the air dryer and the only other thing you will see is small leaks like the one you saw at the fitting. Not saying that is the case with this one, but it is good info on these air systems that will save some time. I agree with the others that any leaks you find it is worth fixing. Just my couple cents!!