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aux compressor runaway

Hi there Foretravelers,
Just noticed when I went to the storage yesterday that my aux compressor was running. Checked the driver air switch and it was off. Had all known disconnects off (1) engine battery, (2) coach by the steps, and (3) house battery bay.

Both air tanks were ~75 psi before I fired up the coach. I ran the coach a few minutes and the aux compressor turned back off. I'm assuming it was trying to get the air pressure up to threshold.

Anyway to keep this from running while I'm not around? Is there something I'm missing?
2003 U320 3820 Designer Series

Re: aux compressor runaway

Reply #1 –
You may have a bad check valve in the system and be "back feeding" your main tanks.  Or a host of other things could cause this issue. Once the air compressor on the engine brought the system up above about 90 PSI your aux compressor cut out switch shut off the compressor, until it falls back down under 90 PSI The AUX compressor is isolated by check valves from the main tanks to preclude the aux compressor trying to keep them up to pressure. The main tanks will usually drift down to about 60 PSI and then a valve at the tank isolate that system at 60 PSI to retain air in the tanks for emergency braking purposes when moving - Best short term resolution is to disconnect the red wire feeding the power to compressor - I have put a "blade style" set of connectors in that line to easily disconnect the compressor - others have put in a switch or an inline fuse for the same purpose until you can determine the cause, disconnect the power to the compressor, as it is not rated for continuous duty.  They are available aftermarket and can be rebuilt, but both are pretty expensive options good luck, tells what you find
Tim Fiedler    2025 LTV Unity MBL on Order
2000 Chevy Tracker 2 Door Convertible 4WD Now lifted 4.5"
1985 Citroen 2CV6 Charleston
Murphy Rebel on wheels with 175HP Titan
Cessna P337
1980 48' Westport MY (!/4 Share)

Re: aux compressor runaway

Reply #2 –
Quote from: RV Mike –
Anyway to keep this from running while I'm not around?
X2 what Tim said.

Simple answer: Locate the power wire to the compressor motor.  Cut the wire and install a manual ON-OFF switch.

Best answer: Figure out why the compressor is running continuously, and correct the problem.

Correcting the problem will require some trouble shooting on your part (or pay a tech $100/hour to do it).

Study the electrical schematic for your coach to learn how the pump is powered, and when.  What turns the compressor on and off?

Study the air system schematic for your coach to learn where the compressed air from the compressor goes, and how it gets there.

Physically follow the actual path of the compressed air and look for possible air leaks or malfunctioning components.

You had other air system problems a couple weeks ago and found a local shop (Blue Moon?) that helped you.  Try them again?

1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: aux compressor runaway

Reply #3 –
Quote from: Chuck & Jeannie –
X2 what Tim said.

Simple answer: Locate the power wire to the compressor motor.  Cut the wire and install a manual ON-OFF switch.

Best answer: Figure out why the compressor is running continuously, and correct the problem.

Correcting the problem will require some trouble shooting on your part (or pay a tech $100/hour to do it).

Study the electrical schematic for your coach to learn how the pump is powered, and when.  What turns the compressor on and off?

Study the air system schematic for your coach to learn where the compressed air from the compressor goes, and how it gets there.

Physically follow the actual path of the compressed air and look for possible air leaks or malfunctioning components.

You had other air system problems a couple weeks ago and found a local shop (Blue Moon?) that helped you.  Try them again?


Have the same issue, PO installed an On/Off Sw.
Prior 2003 U295  40ft  400Hp -Sold
2020 F350 Tremor - Sold
2021 Bundutec Roadrunner - Sold
2017 Airstream Classic - Sold that POS
2017 F250 - Sold
2019 Sprinter Van - Sold
2022 Winnebago Revel 4x4


Army Airborne Vet.

Re: aux compressor runaway

Reply #4 –
As originally wired the dash switch opens a solenoid to the wet tank for the compressor to charge the wet/front/rear tanks.  There was no off switch. If it was 75 psi the compressor would be running.
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: aux compressor runaway

Reply #5 –
Thank you all for your input!

Tim, I did find an inline fuse next to a solenoid on the aux compressor. I waited for it to kick on and pulled to fuse to confirm shut down. Now have to figure out where the leak is. Any idea how many check valves are on the coach? I'm pretty sure I'm not adequately qualified to find, check, and replace them.

Chuck and Jeannie, I would love to get more into self-diagnostics but I'm as of yet still a novice at both the system itself and making time to do so! I appreciate your consideration in reading my initial posts about the air system issues. Thought I had it covered by fixing the air dryer which resolved all problems with pressure, awnings, slides, leveling, etc. Alas, we obviously have leak somewhere...

I called Blue Moon and talked to JJ who thinks the air leak it might be the air bladder(s) as they are originals but wouldn't know of course until I brought it in. Blue Moon charges 175/h, so 100/h sounds pretty good! Of course, the real cost all comes down to $$ spent to efficiency and quality of work vs time spent in the RV.

I'm contemplating holding off for now and keeping an eye on it until after our spring break trip. I'll post back any updates between now and then.

Thanks,
Mike
2003 U320 3820 Designer Series

Re: aux compressor runaway

Reply #6 –
You can add a pressure gauge to the line going to the bladder.  Many add a 90° turn on/off valve before the pressure gauge as well. When your bladder is inflated pressure will be about 11-15 psi.  If it does not hold pressure it might be the bladder or the bladder inflte/delfate manifold.  The valve lets you isolate the bladder to keep air in if the leak is elsewhere or determine if it is the bladder.  It must be open to deflate the bladder.
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: aux compressor runaway

Reply #7 –
Mike, if you think it's one of your bladders, easy way to check is to turn off the air to one of them at the manifold. Each bladder has a manifold with a ball valve to isolate it from the system. They are silver looking blocks which will be in the same bay as the 12 VDC pump. If, after a time your compressor still runs, shut off the other valve and see what happens.
You can PM me if you want.
Richard & Betty Bark & Keiko our Golden Doodle
2003 U320T 3820 PBDS
Build # 6215
MC # 16926
2016 Chevrolet Colorado 4X4 diesel

Re: aux compressor runaway

Reply #8 –
Mike,

I hope I didn't sound harsh or uncaring in my prior post.  I didn't mean it that way.  Dealing with air system problems is part of owning a Foretravel coach.  As you have noted, paying a tech to trouble shoot can get expensive very quickly.  Every new coach owner, at some point, knows nothing about motorhome air systems.  From there, they either take the time to learn how to work on the system themselves, or they make/have enough money to pay other people to work on their coach.  There is nothing wrong with either approach.  Different strokes for different folks.

If you decide to do the work yourself, there are people on this Forum who are more than willing to help you.  The learning curve is steep at first, but it will soon start to make sense.  Finding air leaks, especially, can be tedious and frustrating.  The newer your coach, the more complicated the air system.  Big, serious air system malfunctions can strand you on the side of the road.  Small air leaks are simply irritating...especially if you are the type person who likes to have things "right".  You will likely never find every leak, but you can get the system "tight enough" to satisfy your own standards.  As long as the coach functions correctly and drives normally, small leaks can be tolerated.

Only you know how much time and physical effort you can devote to maintaining the coach.  Do what works best for your situation!
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: aux compressor runaway

Reply #9 –
So I got back to the coach today and the pressure was down to 75 psi again. When I turned the key, the awnings went out? I'm guessing the pressure keeps them in? Once the pressure was up to 90, they closed back up. Good thing as I don't want to drive around with my flaps out.

Chuck & Jeannie
No, I don't take your advice harsh at all. It's where I want to be. Just not there yet. I appreciate every bit of input anyway, harsh or not. I knew going into this that it was going to take some time and patience. I finally got the thing up and going and don't want to rush in and add a new problem and get sidelined again. Thanks for bringing up the fact that air leaks eventually find their way in the system. I can work with that using the whack-a-mole approach. I don't consider myself to have a high threshold of perfection, but it's a real eye opener to learn that most of the important things on the coach rely on pressure. They could just as well called these things Pressure Pushers, as they won't even drive without it!

Richard and Roger & Susan
I'm going to take your advice and mess around with those bladders and see what I find out. Seems like a good place to rule some stuff out. I'll report back what I find.

Thanks,
Michael




2003 U320 3820 Designer Series

Re: aux compressor runaway

Reply #10 –
Also look at the condensate bowl for the aux compressor - possibly the NO solenoid at the bottom of it is fouled and not sealing when the compressor kicks on.  It is supposed to close when the compressor runs and open when the compressor shuts off (to purge condensation).  Ours was notorious for sticking open.  This will cause a runaway behavior.

Also look at the condensate bowl itself it is prone to cracking where the fitting is for the above solenoid valve.  We have even seen a catastrophic failure of a condensate bowl.

You would be able to feel air at the base of that bowl if either of the above are the problem.

This is assuming it isn't a slide bladder - but you should be able to hear a bladder leak if it's that.
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: aux compressor runaway

Reply #11 –
Adding link to post with part numbers for desiccant bowl and NO solenoid

12 volt air compressor will not shut off
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: aux compressor runaway

Reply #12 –
Thanks all for help with the runaway aux compressor on our 2003 U320 . On our spring break trip, had to "unplug" it during the night as I didn't want to disturb neighbors as it would kick on every 2 hrs. The downside is the psi would drop to 75 in the tanks by morning. A few weeks later, I finally have had some time to work on air leak issues.

Methods: checked the aux compressor condensate bowl as Michelle suggested and replaced old dessicant beads. Did not find any leaks here. Ride height was never affected so I assumed the suspension air bags were fine. Did not find any leaks on bladders but did find bubbles on a couple of the brake drain valves on the 3-cock manifold up front. Went ahead and replaced all three with brass Nigo air brake drain cocks and Parker female bulkhead connectors (see below).

Results: Pressure has now held for 24 hrs with aux compressor disconnected. Hopefully this means it will kick on less often. Will test this hypothesis next time we say overnight in it.

Signing off for now. Take care and be safe!

Mike
2003 U320 3820 Designer Series