Compressor/Pump Kicks On Every Two Minutes?? Is This Normal?

[Brewtal66]

Hi Gang,

I just joined the site but have lurked and learned so much over the last few years. I have a 2005 Fleetwood Expedition 38N on a Freightliner XC chassis.

I admit I pretty much know nothing in regards to the air brake system on this rig.

When driving down the road, my front and rear tank pressure gauges will creep down to about 120PSI, then the compressor kicks on and raises them up to about 150PSI before stopping. From the time the tanks are "full" till the time the compressor kicks back on is about 2 minutes.

My question is, is that time period normal? I'm not pushing the brakes or anything, just on cruise control down the highway.

Yesterday I went under it with the tanks full and sprayed every single fitting and hose I could, no bubbles/leaks. This morning I talked with the Service Advisor at a diesel truck repair shop and he said it's perfectly normal, only when you hear a leak or if you turn off the rig and it loses all air pressure within a few minutes should I worry about it.

If the rig is just sitting there idling, or even turned off, it takes a long time for it to cycle though.

So am I over thinking this or am I okay?

Thanks for the help!!

[Jim_HiTek]

I rarely notice my compressor kicking on. My air hovers around 120 PSI after that initial pump up where it goes up to 130 PSI or so. I seem to remember it slipping down to 90 PSI on occasion but shortly after it's back up to 120 PSI.

So, that's how mine behaves, and it takes quite some time for it to lose much air. If mine was doing what you indicate, I'd grab or find the operators guide and read up on operation. Is 150 PSI HIGH for your system? Is it normal during typical driving for it to require a pump up every 2 minutes? Those would be questions the guide might answer.

[Down South]

Sounds like you need to check for air leaks.

[hayward3411]

I think 150lbs is high, my pressure is between 125-110lbs. Not sure about the frequency of compressor coming on but high pressure would cause it. I have a cummins on the same chassis.

[KanzKran]

Automatic ride height valves may be filling/dumping/filling/dumping/etc. as you drive down the road.

And 150 psi cutout pressure sounds high to me, so that's something I'd look into.

Edit: Forget to mention - when driving, the maxi brakes are released, which means they're pressurized. When you climbed under it or just stood next to it, the brakes were probably set, which means no air pressure in those brake chambers (or any other for that matter). So it's possible that you have a leaking fitting or diaphragm in one of those brake chambers, and you won't hear it unless they're pressurized. Chock the wheels really well, release the brakes, shut the engine off, and get out and listen. If you climb under it and it has air suspension, make sure you block the frame so loss of air pressure won't drop the coach on you.

[wolfe10]

When was the last time the AIR DRYER was replaced/major service including valves?


Every two minutes is way too much/too fast for cut in/cut out/repeat.

[Pigman1]

7 step air brake check. If it passes, you're OK, if not you need to get some work done. Do this before you drive. CDL holders are required to do it and RV drivers should too.

https://www.cdl-test.com/blog/how-to...s-cdl-7-steps/

[Brewtal66]

Originally Posted by KanzKran

Automatic ride height valves may be filling/dumping/filling/dumping/etc. as you drive down the road.

And 150 psi cutout pressure sounds high to me, so that's something I'd look into.

Edit: Forget to mention - when driving, the maxi brakes are released, which means they're pressurized. When you climbed under it or just stood next to it, the brakes were probably set, which means no air pressure in those brake chambers (or any other for that matter). So it's possible that you have a leaking fitting or diaphragm in one of those brake chambers, and you won't hear it unless they're pressurized. Chock the wheels really well, release the brakes, shut the engine off, and get out and listen. If you climb under it and it has air suspension, make sure you block the frame so loss of air pressure won't drop the coach on you.

I've been deep on YouTube and just realized this too. Going to recheck it all here soon!

Originally Posted by wolfe10

When was the last time the AIR DRYER was replaced/major service including valves?


Every two minutes is way too much/too fast for cut in/cut out/repeat.

I've never replaced it, but only owned the coach a few years. But when crawling around I did see it and didn't know what it was - saw a video on YouTube of a guy replacing it, so sounds like it's time to do so!

Originally Posted by hayward3411

I think 150lbs is high, my pressure is between 125-110lbs. Not sure about the frequency of compressor coming on but high pressure would cause it. I have a cummins on the same chassis.

I'm going off memory here, it might not be 150 PSI. Thinking about it now, I think that's the max on the gauge but it doesn't ever go that high.

Originally Posted by Pigman1

7 step air brake check. If it passes, you're OK, if not you need to get some work done. Do this before you drive. CDL holders are required to do it and RV drivers should too.

https://www.cdl-test.com/blog/how-to...s-cdl-7-steps/

Going to read that and do that now! Thank you!!

[AnotherMike]

> If you climb under it and it has air suspension, make sure you
> block the frame so loss of air pressure won't drop the coach on you.

ABSOLUTELY!
And use something that can support the full weight of the coach!

Your survivors will thank you.

I lost a friend to a failure to use a jackstand.

Mike

[AnotherMike]

Originally Posted by Pigman1

7 step air brake check. If it passes, you're OK, if not you need to get some work done. Do this before you drive. CDL holders are required to do it and RV drivers should too.

https://www.cdl-test.com/blog/how-to...s-cdl-7-steps/

Originally Posted by Brewtal66

Going to read that and do that now! Thank you!!

Last time I was in the junk store at a truck stop I saw that available as a laminated wallet card for a couple of dollars. The gentleman that i was with (a driver for a trucking firm) said he had one clipped to his sun visor...

Mike

[oh no]

Drain your air tanks an also if you haven't already.Change out the compressor air filter 150 psi is on the high end.Make sure the air dryer not leaking fromo the purge valve

[Brewtal66]

Just to update everyone...I was definitely off on the 150PSI! I was going off the top of my head. 150PSI is the max my gauge reads, but not the max the tanks see.

I did the 7 step brake check and everything checked out perfectly. So I think I'm good and probably over thinking all of this. But I have some peace of mind knowing that everything is working properly.

[KanzKran]

Then it sound's like your air suspension is using air while driving, which is normal.

But do drain the tanks, as water in any tank takes the space of air and will shorten the cycle time, as well as the desiccant in the air dryer. We used to drain the water at the end of every shift back in my driving days, and all rigs had lanyards brought out to where they could be easily yanked on to check for and drain water, if present.

[wolfe10]

Yes, the air suspension does use air, as do the air brakes.


But every two minutes-- something is wrong.


And, opening the tank drains is an excellent idea. They are basically the "report card" for condition of the air dryer. You should only get clean, dry air. Anything else indicated a FAILED air dryer. Worse failure is white powder-- indicating that the dryer desiccant has broken down and is not in your air system.


My recommendation for dryer service is to buy a FACTORY reman dryer. Yes the factory that made it, not a "made to replace" of questionable quality. The factory reman not only has new filter(s), but new valves, heater, etc. Nothing complicated about replacing one.