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vettenuts · 05-29-2023, 01:27 PM

I have been chasing an air leak and just found that I have a fairly good leak back at/near the discharge port of my air drier. I recently had the cartridge changed at Cummins, not sure if it's related because I won't have good access to the air drier until I move the coach later this week and the air pressure loss started a few weeks after the Cummins service.

Both of the my tanks are leaking down simultaneously overnight. After examining the pneumatic schematic I pulled off of DTNA, it appears that there are check valves at each of the black line inlet ports to the tanks from the compressor side of the system. I find it hard to believe that all of the check valves are simultaneously leaking back to the air drier. Not sure what I am missing here and hoping someone might be more familiar with the system can provide more insight.

Has anyone had a leak back at the air drier take down both tanks simultaneously? Just want to make sure I don't have other issues to deal with besides the air drier.

wolfe10 · 05-29-2023, 01:31 PM

Yup, check valve between air dryer and wet tank AND between wet and dry tank(s) are suspect.

Be sure to check the wet tank drain to verify that you don't have any white powder in it. A failed desiccant filter that allows desiccant into the air system can clog a lot of your air system components.

vettenuts · 05-29-2023, 08:56 PM

Desiccant filter was just changed and is changed per Freightliner maintenance schedule, every three years. Drains show no signs of powder or water.

Why would all the check valves fail simultaneously? Something isn’t adding up.

vettenuts · 05-30-2023, 09:04 AM

I did a lanyard pull test (wet, primary, etc.) to determine if my check valves are bad. The tanks held pressure as they are supposed to so my check valves are fine.

However, careful review of the photos of the wet tank and the pneumatic schematic indicate no check valve on the fill port of the wet tank on the line coming from the air dryer. When I drain the wet tank, the secondary and primary remain full and there is no leakage at the air dryer. Noting that the check valves do have an acceptable leakage rate, it may be they are feeding the wet tank over a longer period of time. When I run the engine to refill the wet tank, I do have a pretty good leak at the discharge port of the air dryer.

I think I need to correct the air dryer leak and see if that corrects the problem.

twinboat · 05-30-2023, 09:23 AM

Your wet tank check valve may be on the air dryer outlet. Fix the leak and it may fix the other leak.

vettenuts · 05-30-2023, 05:30 PM

Quote:

Originally Posted by twinboat

Your wet tank check valve may be on the air dryer outlet. Fix the leak and it may fix the other leak.

Yes, I believe that is the case as there is no fittings between the tank connection and the air dryer. The joint that is leaking was disassembled when Cummins did the desiccant filter replacement as they removed the air dryer from the coach. Air dryer was tested for leaks and the problem started about 500 miles later so it may be the hose isn’t fully seated in the push-in fitting and started leaking. Once I get the coach on the ramps to change the differential fluid I will remove the hose, inspect and reinsert. Hopefully that takes care of it otherwise I’ll replace the fitting and trim the hose a tad.

Toribk · 06-02-2023, 09:58 AM

Vettenuts,

That's what I ran into with mine,
the 90° air line fitting coming out of the AD9 was bad and it was quite evident when I sprayed it with soapy water once the coach was aired up.

Keep us posted.

Sent from my SM-G955U using iRV2 - RV Forum mobile app

vettenuts · 06-03-2023, 05:23 AM

I did purge the tanks, removed the hose and cleaned it. The hose appeared a bit dirty so I think it might have been contaminated last time it was assembled damaging the seal. I ordered a new fitting and a tubing cutter to ensure a good cut of the tube as there is very little length to make multiple cuts.

vettenuts · 06-09-2023, 11:33 AM

Hopefully final post on this. I ordered an Alkon brass replacement fitting and a tubing cutter for DOT tubing. I trimmed the end off the tube (leaves barely enough) and installed new fitting. Discharge port connection now passes bubble test. Will wait to see how the system pressure change over time to make sure there isn't another leak I haven't found yet. Hopefully this is the final leak.

vettenuts · 06-10-2023, 06:09 PM

Nope, still have a leak somewhere

Toribk · 06-11-2023, 04:13 AM

Spray your ride height valves as you continue to look for the leak.

I replaced two elbows on the tanks with Alkon fittings and just discovered a third one leaking ever so slightly for the air brake system.

Of course, this fitting is intangled in a hornets nest of air lines and wire loom tie wrapped around it, so changing it out will be a pain in the backside.

Seems these fittings go bad at about the 10 year mark

vettenuts · 06-11-2023, 07:25 AM

I have pretty much finished checking the front half of the system (except parking brake valve) and have not found any leaks. I will be turning the coach around in the driveway this week to back onto ramps (my driveway has a slight slope) so it’s level to change the differential and transmission fluid. I will start looking in the rear at the valves back there that I can’t access as it sits right now with the front on ramps. Sure wish I had access to a lift.

I have checked all the height control valves and they are okay.