Skip to main content ↑ ↓
Topic: 12 volt air compressor comes on now and then (Read 615 times) previous topic - next topic

12 volt air compressor comes on now and then

Just spent 4 days in the FT pulled my 20 foot cargo trailer up to Meeker, Co. for the 4th. All went well. No powerhouse on the steep hills, I weigh in at 32,000 lbs with trailer so good there but 35 mph was average at the top of the grades. 1st time plugged into 50 amp service. Seemed fine. I assume the Heart 2500  does everything on power management when plugged in.. My house batteries went down to 12.2 for one morning then powered back into the 13's for the rest of the trip, but only once?
When working in my shop where the FT is, I'll hear the 12 volt compressor come on for a few seconds at random. I assume this is normal? My air pressure tests all pass. Also once in a while the air dryer will purge itself while driving or sitting at a light. Just a short shot of air let out. Just making sure all this is normal. 2nd time camping and driving it overnight.
Thanks
1996 U295-36, Cummins 300hp, 8.3. Build number 4864. Vin number 1F97D536XTNO54271. Purchased October 31, 2019.

Re: 12 volt air compressor comes on now and then

Reply #1 –
The 12 volt compressor is connected to your leveling system. The computer wakes up every 30 minutes or so and checks to see that all is still level. If not, the HWH computer will try to dump air from the high side. If that isn't possible (you are already on the stops) it will add air to the low side. If you have a slide with an air bladder around it, the same compressor keeps it full. If the compressor is coming on frequently it means that you may have a leak somewhere.

When the big engine is running the main compressor is also running. Air pressure would continue to build, so there is a pressure relief valve built in to the air dryer. Watch your air gauge and you will see the needles slowly drop and then come back up. When they get to the high point you will hear the relief valve open and the shot of air come out. It happens while you are driving, too, but you are too far away to hear it. If you are ever around a big truck you will hear it.

If you are hooking up or unhooking the towed and you have your back turned to it, that's when it will go off. There is a hidden camera there that watches for the unwary. <grin>

Re: 12 volt air compressor comes on now and then

Reply #2 –
Super. Thanks. This FT is growing on me and the cummins smooth power
1996 U295-36, Cummins 300hp, 8.3. Build number 4864. Vin number 1F97D536XTNO54271. Purchased October 31, 2019.

Re: 12 volt air compressor comes on now and then

Reply #3 –
Quote from: dans96u295ft –
1st time plugged into 50 amp service. Seemed fine. I assume the Heart 2500  does everything on power management when plugged in.. My house batteries went down to 12.2 for one morning then powered back into the 13's for the rest of the trip, but only once?


When plugging into any shore power, house battery voltage should quickly go to 14-14.2 VDC with the inverter/charger in BULK mode.  After batteries are fully charged (charging amps drop off) it should drop to 13.2 or so.  If below 13 while on shore power, something is wrong with either the batteries, charger part of the inverter/charger or wiring between them. Start by checking wire connections-- it's free.
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

Re: 12 volt air compressor comes on now and then

Reply #4 –
"Also once in a while the air dryer will purge itself while driving or sitting at a light. Just a short shot of air let out. Just making sure all this is normal."

If your air system has an automatic moisture removal system or "spit valve" - the shot of air is oftentimes the spit valve purging air to ensure that any moisture build up is shot out of the tank. Some older systems require manual moisture dank drain. You also have a relief valve if the governor fails and over pressures above 150psi. Our old fire trucks required us to do daily/weekly tank moisture drain checks. By opening pet-cock valve. 

Re: 12 volt air compressor comes on now and then

Reply #5 –
Quote from: dans96u295ft –
. Also once in a while the air dryer will purge itself while driving or sitting at a light. Just a short shot of air let out. Just making sure all this is normal. 2nd time camping and driving it overnight.
Thanks

As said by pibutler, this is NORMAL.

Your on-engine air compressor does not "make air" all the time.  The air GOVERNOR turns it on (actually, just closes the exhaust valve(s)) when pressure drops to CUT-IN PRESSURE.  And turns it off (opens compressor exhaust valves so it is doing no work/taking minimal HP) when CUT-OUT PRESSURE is reached.

Said another way, your air pressure will range between the two, not remain steady.

Time between ON cycles depends on air usage by air brakes and suspension (and of course any leaks!).
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

Re: 12 volt air compressor comes on now and then

Reply #6 –
Sounds like it did have an issue at 12.2 plugged in but is working now. Everything else is ok. Thanks
1996 U295-36, Cummins 300hp, 8.3. Build number 4864. Vin number 1F97D536XTNO54271. Purchased October 31, 2019.

Re: 12 volt air compressor comes on now and then

Reply #7 –
Quote from: dans96u295ft –
Sounds like it did have an issue at 12.2 plugged in but is working now. Everything else is ok. Thanks

No speculation-- you DID have a problem when house battery voltage at 12.2 VDC when plugged in!  Keep an eye on it and be sure to tighten connections at inverter/charger, slow burn fuse and batteries.
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

Re: 12 volt air compressor comes on now and then

Reply #8 –
My x Foretravel mechanic carefully soaped all our  air bags and lines and fixed all of my systems leaks 8 years ago.

Once leveled it has never moved.  I am able to turn off the panel.  If you have small leaks the panel if left on checks for level every 30 minutes as was posted and will relevel your coach. If an "up" command is sent to the suspension system the air compressor comes on to augment the air needed.
"Riding and rejoicing"
Bob
1997 U320 40' Mid entry, build 5132,  wtbi ce27, 4th owner
2007 Solara convertible
2 prodeco tech outlaw ss electric bikes

1095 watts solar
08 Ls 460 and a sc430
2000 Ford F-250 superduty 4x4

Re: 12 volt air compressor comes on now and then

Reply #9 –
It has always worked plugged into 110v-20amp in my garage. When at the park at 50 amps was when it got confused. One day out of 4. I'll keep an eye on it. I'll be camping again later this month, same place. Thx
1996 U295-36, Cummins 300hp, 8.3. Build number 4864. Vin number 1F97D536XTNO54271. Purchased October 31, 2019.
 

Re: 12 volt air compressor comes on now and then

Reply #10 –
If there was an issue with the 50 amp power-- you may have other damage.

ALWAYS check shore power!  No idea if someone before you ran over the box, if Bubba wired it, if the box went under water............

Your inverter/charger has no way of knowing whether you are plugged into 15 amp, 30 amp or 50 amp-- assuming each is wired correctly.  All the inverter/charger sees is ONE HOT, ONE NEUTRAL, ONE GROUND.  120 VAC between hot and neutral or hot and ground.

 
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