Skip to main content ↑ ↓
Topic: Air dryer purge with engine off (Read 572 times) previous topic - next topic

Air dryer purge with engine off

This is probably nothing to worry about, but I'll put it our there as I've never seen it before.  We parked, cut the engine got all set up and settled in.    About 25 minutes after shutting off the engine, I was outside and heard what sounded like a slow pressure build then then the air dryer purge valve popped off but with much less force than when the engine is running.  Can't hear any leaks since, coach is holding pressure, and don't see anything that looks out of place under the coach.  Keith did the regular air dryer service a couple month ago.

Anyone seen this before and should I be concerned?
Joe Phebus and Jaime Trujillo
2002 U270 3410  Build: 5953 Motorcader # 18595
2100 W Solar, 600 AH Battleborn Batteries,  Victron Multi-Plus II 3000 Inverter, Cerbo GX, & MPPT Chargers
1992 Geo Tracker

Re: Air dryer purge with engine off

Reply #1 –
Joe, are you sure it was the air dryer purging ?  Did you have the Auto-Level set ?  It might have been the Level System coming on and leveling the coach by draining some air from an air bag.  It gives that same swoosh sound of air, just not quite as loud as the dryer.  Maybe??
Mark & Bev
2001 U295 36' Slide
Cummins ISC 8.3 350HP
Build #5802
Jeep Wrangler Toad

Re: Air dryer purge with engine off

Reply #2 –
Mine does that for as long as I can remember. Usually about 5-10 min after shutdown.
Bruce, Linda, and Macy
Zoey RIP 1/20/19
1999 U295 40' build #5400
2017 silver Jeep Wrangler, 1260 watts of solar on top
Moving around the country

Re: Air dryer purge with engine off

Reply #3 –
Quote from: MarkC –
Joe, are you sure it was the air dryer purging ?  Did you have the Auto-Level set ?  It might have been the Level System coming on and leveling the coach by draining some air from an air bag.  It gives that same swoosh sound of air, just not quite as loud as the dryer.  Maybe??

+1, especially with the roughly 25 minutes (let's call it 30) after engine shutdown.  That would correspond to the first wakeup cycle of the leveling system to check for level, and it's not unusual for some settling to have occurred as things cool down from the drive.
Learn every day, but especially from the experiences of others. It's cheaper!  - John C. Bogle

2000 U320 36' non-slide / WildEBeest Rescue
2003 U320

Re: Air dryer purge with engine off

Reply #4 –
Quote from: MarkC –
Joe, are you sure it was the air dryer purging ?  Did you have the Auto-Level set ?  It might have been the Level System coming on and leveling the coach by draining some air from an air bag.  It gives that same swoosh sound of air, just not quite as loud as the dryer.  Maybe??

Definitely not the auto-level.  I know that sound.  It could have been something other than the air dryer, but the force was enough to blow some dust.
Joe Phebus and Jaime Trujillo
2002 U270 3410  Build: 5953 Motorcader # 18595
2100 W Solar, 600 AH Battleborn Batteries,  Victron Multi-Plus II 3000 Inverter, Cerbo GX, & MPPT Chargers
1992 Geo Tracker

Re: Air dryer purge with engine off

Reply #5 –
Our GV does the same thing.
Hans & Marjet
1995 U300 "Ben" (#4719)
3176B Cat,4060HD,Jake
SKP#139131
Motorcade#17579
2006 Honda Element (towed)

Re: Air dryer purge with engine off

Reply #6 –
Wonder if there's a check valve in the system that's leaking back and over-pressuring the air dryer relief valve?
Learn every day, but especially from the experiences of others. It's cheaper!  - John C. Bogle

2000 U320 36' non-slide / WildEBeest Rescue
2003 U320

Re: Air dryer purge with engine off

Reply #7 –
Quote from: Michelle –
+1, especially with the roughly 25 minutes (let's call it 30) after engine shutdown.  That would correspond to the first wakeup cycle of the leveling system to check for level, and it's not unusual for some settling to have occurred as things cool down from the drive.

The auto-level is an instantaneous dump of air, and it a typically a different sound.  We auto-level a lot and I've never seen it blow dust..  The lead-up sound then dump similar to the air dryer makes me pretty certain its not auto-level

I'm thinking settling is a good diagnosis, maybe back pressure from the airbags.  Or maybe it way just right on the edge when we shut down and the settling in caused it to pop.
Joe Phebus and Jaime Trujillo
2002 U270 3410  Build: 5953 Motorcader # 18595
2100 W Solar, 600 AH Battleborn Batteries,  Victron Multi-Plus II 3000 Inverter, Cerbo GX, & MPPT Chargers
1992 Geo Tracker

Re: Air dryer purge with engine off

Reply #8 –
Quote from: Michelle –
Wonder if there's a check valve in the system that's leaking back and over-pressuring the air dryer relief valve?

On your age coach along with the others in this thread this is possible.
On the dryer if it has the isolation valve there should be a 1/4" line that comes off and heads to the front. It may be tagged 60. This line terminates on the wet tank with a 90^ fitting. That 90 should be a check valve. Hard to get to, hard to find, YES If the coach has this system and that check valve leaks will it cause these symptoms? Yes

Mike
Pamela & Mike 97 U 320

"It's not what happens to you, but how you react to it that matters."

Re: Air dryer purge with engine off

Reply #9 –
Flatulence!
Tim Dianics
Pam Sapienza
Vader PupZilla Labrador Canine Beast (AKA Pup)
Columbia, MO
1996 U320 4000
2021 Jeep Gladiator, Diesel

Re: Air dryer purge with engine off

Reply #10 –
Along the lines of what Michelle said. 10 or 15 min after shutdown I  will hear an air wonderment and it will do it once and it isn't purge. Some things we may never know the technical  answer to but I wouldn't be concerned.
Dub McBride 1996 270

Re: Air dryer purge with engine off

Reply #11 –
Could also be heat soak (dryer in engine bay)-- rise in temperature> rise in PSI.  Rise in PSI could exceed cut-out PSI.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020