SOLVED: Bus Won't Air Up

[GnarlyBus]

We're on the road heading north and after lunch the bus won't air up. This issue happened this morning but seemed to go away and start normally after I messed with the parking brake push-pull valve. I figured that I hadn't set it correctly the night before but here we are again.

The air bags are still full from when we parked, but the bus doesn't build air on the dash gauge (maybe very slowly). I can hear air coming from between the front wheels. Maybe louder from the passenger side. I checked the air dryer and it's not the problem.

It seems like something is stuck open but I'm not sure what or how to reach it.

What can I do next? Thanks!

[buswarrior]

Turn wheels all the way one way, check both sides, turn all the way the other way to improve access.

Keep looking, listening and feeling around.

Everyone is just going to start listing all the parts under the front end, still won't find YOUR leak...

Happy coaching!
Buswarrior

[GnarlyBus]

It is totally the air dryer stuck open at the bottom. I thought something much smaller under the drivers seat was the air dryer.

Any tricks to make it close so I can get on the road?

[GnarlyBus]

Used search and found that I can tap it closed and service it later? Here's a pic. Tap the brass piece at the bottom?

[GnarlyBus]

I cleaned it all up. I also noticed the air dryer heater connection was broken (maybe by me when pulling the boot off) so I repaired that. How does the heater work? How do I "turn it on"?

[Utahclaimjumper]

It comes on with the ignition.>>>Dan

[GnarlyBus]

Thanks! I'm back up and airing up! See y'all down the road! Scheduling an air dryer rebuild/purchase tonight!

[GnarlyBus]

I got to where I needed tonight. Whenever I stopped the bus, the purge valve would open for a minute or two before closing again. After looking at pictures online (see attached) I realized I'm missing a rubber stopper on the purge valve. How is it even stopping leaking if this is gone?

[Dave5Cs]

That is just an air deflector. The purge valve is behind that. What generally happens is people don't maintane their air dryer each year or two and all the crap come through it and water then the stuff gets blown out the end when the psi reaches 120 and stuff gets stuck in the port on the bottom and won't allow it to close some even get rust in there because their heater is not working. Some work when you turn your heater on and it gets to a certain temp.

[buswarrior]

Glad you're functional.

Check the schematic, most of that era, the air drier heater was powered by the coach heat switch, an inline fuse holder on the wire with a glass fuse in it tucked into bottom of the outside under driver's window electric panel.

Unwittingly, busnuts tear out the coach HVAC, never turn on the switch in the cold, and no power to the air drier. Seated coach with air leaks, left idling in the winter with the coach heat turned off to keep the engine temp up would freeze up its drier too.

The heater has its own thermostat, nothing for you to do, except confirm there's power to it.

The rubber disc is to keep the critters from getting in, and let the blast of purge get out. Mud daubers and those small wasps that use mud to lay their eggs in small places are the devil for a sitting air system...

Good that you are planning service soon, air driers don't get better by themselves, and the tapping trick only works for so long...

Happy coaching!
Buswarrior

[GnarlyBus]

Thanks for the note on the heater wire. I was wondering about that. I read a thread where it talked about the wire being powered by the HVAC system which is totally gone from my bus. I'll check power to it and look for that 3A glass fuse tomorrow. Just in case I need to run a new wire, it's 24v, right?

I'm glad the deflector isn't crucial. Once I get it on the road, it purges at 120 and kicks back in at around 90. So does that rule out issues with the governor/hoses from there?

[buswarrior]

The cycle sounds fine. I think you've found your issue.

Yes, the purge valve heater is 24 volts, and be sure to remind your service technician, as 12 volt heaters predominate out in our mostly 12 volt world. You need the right one put back in!

When checking that wire to the air drier, don't fool yourself that it has no power, if you haven't got the coach into the proper configuration to give it power.

HVAC won't turn on until low air goes out, and alternator starts charging. I can't remember if the air drier wire is connected before or after that big relay.

Happy coaching!
Buswarrior

[bevans6]

If you have the correct sized wrench (I used a small pipe wrench) you can remove the purge valve, clean it up, lubricate the O-rings a bit and it might keep working for a while.  You can also buy a rebuild kit, and replace the soft parts for a proper fix.  The kit is Bendix part number 287053N for an AD2 purge valve kit.  The correct sequence of events is this:  Air governor is in cut-in mode, air system is filling, air signal from governor to purge valve is zero PSI.  System fills to cut-out pressure, governor switches to cut-out mode, governor sends a line (90 psi at that point) pressure signal to the compressor and to the purge valve.  Air pressure opens the purge valve, exhausts the air inside the air dryer, and holds the purge valve open until cut-in and the cycle starts again.  The normal failure mode is the purge valve sticks open when the air governs switches to the next fill cycle, it ignores the high pressure signal and does not close.  Hitting it with a stick jars it loose.  If it does it once, it will do it again, so at least clean/lubricate it.

[lostagain]

I installed a switch on the dash to turn the dryer purge valve heater on or off. I like manual things. To test the heater, the temperature has to be below freezing so the thermostat turns it on, regardless of how it is powered upstream.

JC

[GnarlyBus]

I went ahead and wired it to ignition this morning with a fuse. Starting the bus up soon. Hope to be rolling down the road again today.

I appreciate all the responses!