Coach not building air in subfreezing temps.

[Scott & Heather]

Hi Gents,

We sadly have only put about 2000 miles on our brand spanking new Leid Diesel Engine. It runs unbelievably well. Doesn't leak a drop of oil, (literally not a single drop) and dynoed at 550hp. It runs so cool now that I have to block off the radiators to get it up to temp. It's kinda life changing having a solid power train as a fulltimer. So here's my issue at the moment: we've had super cold temps here in Michigan. Started coach today and it won't build air. Compressor is working, and I can drain the rear drain at the engine compartment door with plenty of pressure. But air not building on gauge and can't fill rear or front bags. I obviously have something frozen somewhere and was hoping you could point me towards the most likely trouble areas. For reference, I have a brand new compressor (2000 miles ago) with a brand new governor and new associated air lines and compressor is indeed building air. But I can hear it cycling constantly. Doesn't stop cycling.

[buswarrior]

Air drier purge valve is frozen open, air won't pass.

Purge valve heater wire powered?

Pan of charcoal under the air drier, shield with whatever to block the wind, see if you get some action in a little while?

Happy coaching!
Buswarrior

[sledhead]

you might have to wait for the weather to warm up and try it again and then drain all the tanks as there is probably some moisture in the lines or tanks that has froze . you could be lucky as when that happened to me the line burst and that was a pain in the azs to fix in the - 15 cold outside . it is going to warm up in the next few days

dave   

[Scott & Heather]

So I need some schooling in the air system. My air purge valve has frozen before (heater wires are connected but it apparently doesn't work. I was able to thaw it. But I did build air when that was frozen. It just never purged. So do I need to chase down something else?

[lostagain]

If the air line from the compressor to the dryer has a low spot, that could be frozen. BTDT.

[belfert]

When the purge valve froze on my AD-9 it blocked all air getting through.  My issue was buying the wrong voltage rebuilt purge valve.  A rebuilt purge valve is fairly inexpensive if yours is broken.  I also replaced the cartridge on my air dryer as I figured it might be full of moisture.

[buswarrior]

When a typical Bendix air drier is signalled to purge, when the purge valve is open, the throughput from the compressor is "closed" to the rest of the system.

In the absence of a working heater, the valve freezes in place, and will not return to closed when the air pressure seeps away.

Then the engine gets started, but the  air can go no further than the air drier. You get huge air pressure at the discharge muffler drain down the back, typically the compressor governor sense line is somewhere beyond the air drier, sensing no air pressure. The safety valve mounted in the drier, or close to the compressor will let off pressure periodically.

And, of course, little or no air pressure builds on the dashboard gauge, and no functionality. The mechanical engine crowd might not even be able to shut the engine off, no air for the controls...

Usually this phenomenom is while the coach has been parked. Sometimes, while driving in very cold weather, but the heat of the operating compressor, sending warm air into the drier keeps things barely working, unless in the arctic.

It won"t be very much moisture, a lick on the seat will prevent the valve from moving.

It won't take very long to get it to release, with some heat under it, or if the coach was dragged into a shop.

The defence is very easy. A busnut should know the age of their air drier purge valve, the heater is integrated in the end piece, replace it if unknown, along with a fresh desicant cartridge or stuffing. An annual check of the heater wiring, usually in the fall, replace the wire if it looks sketchy, and you are good to go for the coming winter, and several more, in busnut duty.

Drain the discharge muffler down the back every day that the coach is operated all year long, and enjoy a dry air system, and no winter problems.

Happy coaching!
Buswarrior

[lvmci]

Magnetic oil pan heater, mine for my 1950 f1 pickup, might be a quick fix to plug in and bring above freezing...

[tr206]

It is probably your air governor supply line iced up, your governor activates your compressor to pump air you need to thaw it out with heat and/or air line antifreeze. The line should run from a air tank to the governor also when its thawed drain the water out of the air tank or it will happen again. Good Luck.
Here is a air system diagram link. https://www.google.com/search?q=air+governor+diagram&client=opera&hs=YO0&tbm=isch&source=iu&ictx=1&fir=AQkZkBj8UmFTBM%252CZKUiJASCIepi6M%252C_&vet=1&usg=AI4_-kQgPSktXXAlP9FUqA6KE-RFY3Lu1w&sa=X&ved=2ahUKEwig7ejNhfXuAhXVaM0KHYjxAjQQ9QF6BAgPEAE&biw=1240&bih=659#imgrc=AQkZkBj8UmFTBM

[Knuckles]

Take the line off the compresser and pour some air line antifreeze in it till its full  hook back up and give it a few minutes  thats what we did when trucking way up north in Canada. If that doesn't thaw it quick enough we got an elbow from a wood stove on the ground under the air drier and put a propane tiger torch in the end of the pipe. As long as the end of the pipe is a foot or so from it nothing should melt except the ice.  Shouldn't take too long and you should be good to go  In the old days pre air dryers you had a tank you filled with air line antifreeze and it ejected it in the air system constantly and that worked very well. My 4107 still has one and i've used it quite frequently   Hope this works for you

[buswarrior]

Air line alcohol is a defensive product, not an offensive one. It needs to be used ahead of time, if one chooses to use it.

There are multiple problems. I list them here for expanding the knowledge base as counter point.

First, Bendix has recommended against any use of it for decades now. It rinses lubrication from air valves, leading to earlier functionaility problems. Back in the day, we had no choice. With an air drier, there is no further need for it.

Next, physics. AIr line alcohol won't melt what is frozen, it has to mix with the moisture to stay unfrozen.

The "saves" atributed to its use are usually dependant on the alcohol being warm, from being inside somewhere.

And if the way is blocked, it can't get there anyway.

And alcohol will turn the air drier desicant into a mud, rendering it useless for drying the air, and the resulting sludge will then foul up the purge valve.

If it is being added to a system with an air drier, pumping it into the tanks with them drained, via a drain valve fitting is a better strategy, but won't help a frozen purge valve.

Frozen governor lines is unlikely, the compressor is running, and the absence of an air signal is what triggers the purge valve to close. The purge valve is staying open, blocking the filling of the system because it is locally frozen.

Appling heat to the bottom of the air drier is by far strategy number one, and the purge valve heater will be found to be broken or unpowered.

Every busnut with an air drier who does not know what circuit powers their air drier purge valve, and does not have a fall inspection strategy to confirm, is going to be frozen up, at some point, due to this exact problem.

Go back and check the archives both here and on BNO, january and February are regularly peppered in exactly the same symptoms, and exactly the same responces.

We do it to ourselves.

Please, busnuts, break the cycle of winter air diablement, check and replace that purge valve and its heater!

Happy coaching!
Buswarrior

[dtcerrato]

What buswarrior said...

[chessie4905]

AND most don't heed. As soon as it thaws out, forgotten till next winter, repeat like Ground hog day. Majority with freezing issues won't pony up for an air drier. "I drain my tanks frequently". If it works for you all the time, fine. Or they have an air drier and never service it. Fine. We'll still be here offering our advice and opinions.

[6805eagleguy]

I am thinking about a air dryer... not sure the pros and cons tho.
I have one at my disposal, to put on , or leave off. Thoughts?

[buswarrior]

I am thinking about a air dryer... not sure the pros and cons tho.
I have one at my disposal, to put on , or leave off. Thoughts?

Install. You have one, a nice project for some day in the nice weather.

Every new vehicle, for decades, comes with one standard for good reasons.

Install religiously according to recommendations, maintain the drier, all your moisture related problems go away.

Happy coaching!
Buswarrior