Air system purges/cycles every 40 seconds

[ShoreRider]

This is my first post to this forum. I have been on here nearly 1.5 years and was always able to to find a thread that was sufficiently similar to my problem to find a workable solution, so I never posted before.

I have a 2005 Fleetwood expedition with a Cat C7 engine. Every 39-40 seconds, the Air drier purges This is at low idle (750 RPM). it does not matter whether the air suspension is activated or not. The console gauges for the primary and secondary tank never move, at least that I can detect. they will hold airs for days. I searched this forum and found this thread which is very relevant:
https://www.irv2.com/forums/f115/air...ds-383403.html

It contained a good exchange of info and ideas in both directions. I followed this thread to its conclusion. I rebuilt my Haldex PURest air dryer lower half and replaced the desiccant cartridge. Unlike that thread, the original purge valve was completely intact, so that was not the problem The output check valve was seating properly when I disassembled it so that was not a problem either. I was careful in the rebuild. After re-installing the dryer, the same symptoms again with the same 39 second interval. Actually the original timing before air dryer rebuild was 36-37 seconds.

I then removed the wet tank manual drain valve, installed a male quick connect air fitting on the wet tank, and then attached my tire fill guage which has a female air coupler so I could monitor the wet tank pressure (sorry for the verbosity). Here is what I observed with engine speed at 750 RPM (low idle):

• 18 sec - deplete wet tank from 126 PSI to 110 PSI
• 16 sec - hold pressure at 110 PSI
• 6 sec - fill from 110 PSI to 126 PSI

All pressure in whole digits, total time adds up to 40 sec. due to rounding. This repeats continuously.

I then shut off the engine and the wet tank pressure settled at 110 PSI. 10 minutes later, it was still at 110PSI. After 40 minutes, it was at 107.5 PSI so I leaked a mere 2.5 PSI. I take this to mean the 18 second air depletion from 126 to 110 PSI while the engine was running is not the result of an air hose or fitting leak.

Any Thoughts on what is happening? Does this point to the Governor? It is marked "T-293975-H"; I believe this is a Bendix P/N. Google only got me to used, NON-reman'd units on E-Bay (looked worse than mine) for an exact match and lots of links to other D-2 type governors with different P/Ns. I did find this "quickrefguide.pdf", see page 16. Mine looks like a non adjustable D-2A type, but the Part numbers don't match the attached PDF. I could not find a cross reference. Anybody have ideas how to cross reference this?

Other questions:

1. The Air Dryer has a schrader valve on the bottom. Can I use this conduct further tests? How?
2. Any other test I can run before I start another "parts chase" that turns out not to be the solution?

Thanks

[twinboat]

Just about any D2 governor will work.

Did you look all over the wet tank section for a pressure protection valve.

They provide air to accessories until the tank pressure drops to a set limit. Once that limit is reached, they stop air flow to the accessories to preserve the air for braking. Look like a small gas regulator.

The only other thing that comes to mind is the 1/4 inch lines having damage somewhere. One runs from the governor to the air dryer purge control.

If your governor is not bolted to the compressor, there will be another between the compressor and governor.

If all looks good, bypass the dryer and plug the 1/4 line at the purge valve end. See if the wet tank holds steady pressure.

[twinboat]

Thought about it more.

The governor sends a air signal to the purge valve and compressor valves when wet tank pressure is reached. That signal pressure remains to keep the purge valve open, so moisture can drip out.

At about 110 psi, it stops sending the signal to close the purge valve and compressor valves, so it can start to refill the tanks.

It's possible that the 1/4inch line, between the governor and purge valve, is leaking. That leak would stop leaking once the governor calls for air again.

[ShoreRider]

Twinboat:

Thanks for your input. I did look all over the wet tank. It only appears to be about 6 inches long not counting the end cap (does this sound right?) of the primary tank. There was Tee that took one 1/2" hose to the back side of the same tank (primary) and one 1/2" hose that went to the secondary tank. There was another Tee that had the 1/4" control hose to the governor and a pressure relief valve. I saw no PPV. I have attached an air system schematic that I have been been using. I don't believe it is exact representation of my system, more like a "road map with a couple of streets missing". It shows 2 PPVs attached to the secondary tank at grid B4/B5 intersection, which makes sense. So any accessories would drain the secondary tank.

WRT 1/4" control hose having damage, I still can't get past the fact that the Wet tank depletes and then holds pressure for at 110 PSI for 16 sec. If it leaked, it would continue to leak throughout. The only way for the wet tank to deplete is through the 1/4" line to or through the governor, right? the primary and secondary tanks are full and don't leak, the air dryer has a check valve that was good before and now is new and the drain outlet has my own gauge on it.

My governor is mounted separately away from both the compressor and air dryer. As you described, it has a manufactured line (swaged fittings) from the compressor and a 1/4" nylon terminating at the unloader ports, and a 1/4" hose from the wet tank to the reservoir port. The exhaust port appears to have an outward facing check valve; definitely not a fixed plug.

If I were to bypass the air dryer altogether and plug the 1/4" line at the dryer with golf tee like the OP in the thread I referenced in my first post, I could end up with out any head unloading capability if the tee "popped out" like the OP described happened to him. Under that condition, wouldn't the control signal from the governor unloader go to near zero PSI? And then I would have no head unloading on the compressor at all. This all presumes the governor is still mostly or partly functional. Am I understanding the functionality of the governor correctly?

From your second post:

It's possible that the 1/4inch line, between the governor and purge valve, is leaking. That leak would stop leaking once the governor calls for air again.

I will look at this closely. On the coach, i could use soapy water at the push-to-connect fittings. I could probably remove that completely from the coach, then inspect and bench test it if I could not see an issue while installed.

Sorry for all the questions, I am trying to reason my way through this all, before I take wrench to any 17 year old fittings and break anything else.

I ordered a D-2 governor on line that should be a workable replacement and will install it weather and time permitting as soon as possible.

Thanks again

[twinboat]

The only time there is air in the 1/4 lines to the compressor unloader valve and dryer purge valve is when air is up to 125 psi or your cut off pressure.

As pressure drops and gets to the point where the tanks need refilling, the governor stops sending air out and vents the air from both lines. It may be when your leak stops. They won't leak if the governor is calling for air.

You need to take a hard look at the two lines, one to the air dryer and one to the compressor head.

The governor ehxaust port probably has a filter not a check valve.

[Gary RVRoamer]

I think twinboat is on the right track.


I had a similar problem when I first got my used coach, but I don't know exactly what fixed it. I stopped at the Freightliner Factory Service Center and they went thru the entire air system. They said they found multiple leaks plus the air dryer had never been serviced. When they got done, no more extraneous purging.

[ShoreRider]

Gentlemen:

I went around to the daubed leak detection fluid on both lines connected to the governor unloader port. The Push to connect fitting at the air dryer leaked significantly, almost violently right after the dryer purge valve opened and for about 18 seconds afterwards. Air continues to trickle out of the purge valve for this period as well. It is my understanding this is normal operation of the purge valve. The leaking stopped until about 20-22 seconds later, at which point the cycle repeated. It was good I had eyeglasses on to protect me from the leak detection fluid spraying around. I ordered another PTC fitting from NAPA for pickup tomorrow. Hope this fixes it; I will follow-up ether way.

Thanks for your assistance on this issue.
Chuck

[96 Wideglide]

Originally Posted by ShoreRider

Air continues to trickle out of the purge valve for this period as well. It is my understanding this is normal operation of the purge valve.

Likely the regen cycle!

18 seconds seems kinda excessive thou! After purging, I believe mine regens for about 9-10 seconds.

[twinboat]

I think you found your problem.

[ShoreRider]

Success. So I replaced the PTC connector at the air dryer. When I examined the end of the tubing, it had a narrow V-shaped gash in the part of it that was inserted into the push to connect fitting. I did not see this when I removed the tubing from the PTC so I could unmount and rebuild the dryer. I may have caused this when I reassembled. Or not. In any event, I clean-cut the tubing, reinserted, cranked up the engine and no more cycling. After the wet tank filled and pressure settled out for a couple of minutes, I observed I lost approx. 1 PSI over 14 minutes. I think we can conclude this thread. I will check this again in the spring.

Thanks Twinboat

Thanks Gary

Thanks 96 Wideglide

Regards,
Chuck