Any ideas for fixing cold weather problems with air compressor?

[luvrbus]

You must have a cold weather leak some place cold air compresses faster than hot air so I was taught in school


good luck

[belfert]

You must have a cold weather leak some place cold air compresses faster than hot air so I was taught in school

The safety valve on the compressor is releasing air constantly so I suspect a blockage more than a leak.  I do have some cold weather leak somewhere as the air will drain out in a few days in cold weather, but air will stay up almost forever in warm weather.

I'm going to try a few more things before I give up and call in a mobile mechanic.  I will take the bus in for a checkup on the air system once I get the air system flowing again.

[zubzub]

you sure it's not the safety valve itself?

[luvrbus]

So what you are saying is your system has a discharge line safety valve if so those are designed to work when the line is frozen so like Pat said it maybe bad they cost around 20 bucks new change it.


good luck

[belfert]

I've talked to several mechanics about this.  I'm not certain I have a safety discharge valve, but I probably do.  The interesting thing is that everything works fine above freezing.  I had this same problem the last time I tried to run the bus during freezing weather.  That time I was able to run the bus at high idle until the engine warmed up enough to warm up the compressor and it started working.

I have more investigation to do tomorrow to see if I have a safety discharge valve.  I will also be removing the air dryer to replace the cartridge and the purge valve.  I will check to see if the line going into the dryer is froze up or not.

[Busted Knuckle]

Brian,
If you have much moisture in the system you've already found the problem!
Moisture freezes in cold weather! Frozen moisture gets stuck in valves and holds them open where they leak. When they are leaking air won't build!
When you told us earlier that you were pretty sure that it wasn't a moisture issue as you had serviced the air dryer & had automatic drains I skipped this train of thought! ( by the way I hate automatic drains because when they get a little age on them they are more trouble that they are worth! )
FWIW
  BK 

[buswarrior]

I wish I could be paid for this....and all the unnecessary maintenance you are about to pay for.

It works warm, it doesn't work frozen?

Settle down, get the PROPER parts installed and connected, system fired up...

And then the problem will be gone.

Read up on exactly what the innards of an air drier does. The purge valve, while FROZEN in the purge position, plugs the compressor output.

That is why the grizzled veterans of the coach and truck industry who went before, and I have repeated on these boards, that when parking the coach in the cooler months, lower the air pressure down to where the compressor is pumping before you shut down, so the purge valve can freeze in a good position, not a failure position.

In summary, returning to the issue at hand, a frozen purge valve prevents air going beyond the drier, the air pressure keeps building until the compressor can't squeeze it any higher, or something lets some air out.

I will collect in Arcadia.

happy coaching!
buswarrior

[belfert]

The interesting thing is I pulled the purge valve and started the engine after that.  I thought air would free flow out of the air dryer, but still the same problem as before.

The main issue with the purge valve is that I bought the wrong voltage unit the last time I replaced the purge valve.  My coach is primarily 24 volt so I just assumed the air dryer is 24 volt.  It turns out to be 12 volt and the 24 volt element was probably generating little or no heat.  I have a replacement 12 volt valve I will install this afternoon.  I'm also going to replace the dessicant while I am at it.

I had replaced the purge valve and dessicant last about 15,000 miles ago, but it was three or four years ago.

[buswarrior]

So, the coach has been through a number of winters before this failure occurred?

Kinda important info for accurate troubleshooting...

Let the enlightenment continue!

happy coaching!
buswarrior

[belfert]

The coach has never compressed air properly below 32 degrees in the winter since I've owned it.  The one other time I ran the coach in the winter I let the engine run on high idle for 30 minutes and it started working once the engine warmed up.

I got the air compressor issue fixed, mostly!  I pulled the intake line off the air dryer and it was plugged with ice.  I heated it for a bit with my heat gun and then started the engine.  A 2" long plug of ice blew out of the line and air came rushing out like it should.  I removed the air dryer and brought it in the house to that out before I replace the dessicant and the purge valve.

It seems all my problems started because I put in the wrong voltage purge valve.  I'm going to hopefully get the air dryer put back in today.  The governor was never the problem like someone told me.

[Busted Knuckle]

Brian moisture in the airlines become "A 2" long plug of ice" and cause the ill effects you are experiencing.
As long as Ice is plugging the line it will never work properly!
What happened before it not so much that you ran the engine @ high idle for 30 mins. But rather the heater worked for 30 mins supply warm air until the ice melted! (no heater = no melt!)
  BK 

[buswarrior]

The next frontier, you've got wet inside the system, and your next post will be lost functionality due to frozen valving. On your way to Arcadia

You need some brake alcohol pumped into the tanks.

Also, the automatic drain valves on those other tanks...
They don't work as advertised, and you want to see what is, or isn't, accumulating in your tanks.
Dump them for cable pulls and one knee on the ground, peer underneath when you pull to see what doesn't come out.

I posted extensively on recovering a polluted air system a couple winters ago for a busnut that the previous owner messed everything up. Ignore the out of context bits:


An outboard motor fuel line with the primer bulb, a female airline connector substituted in the outlet end, open pipe on the inlet end goes into the gallon of brake alcohol. Hold on to the fittings you cut off, someone will want them for the boat. And a couple gallons of brake alcohol.

The drains on every tank get replaced with a male airline fitting and a quarter turn valve. (This also makes taking pressure readings with a tire gauge and filling with the shop air an easy routine.)

Drain the tanks of air and whatever else will come out, and then pump a quarter to a half gallon of brake alcohol into each of the air tanks. You have 4 stock, one ahead of the rear axle, two behind the front axle and one up under the driver. If you find other places to store air.... well, I wouldn't be surprised, someone has been playing with it already.

Start bus, go for a drive, operate all air system components repeatedly, seats fill and empty, wipers, washer, brakes, service and parking on and off a dozen times or better, front door air lock. still have the radiator shutters? Go and use the bypass valves to run the air through and through out the system. Air horn? The air suspension is the devil, hard to get flow though that without having access to the height valving. Hope for the best on this one.

Leave the alcohol in the other tanks until spring, now, drain the wet tank, if you don't like the colour of what comes out, get your trusty primer bulb rig and pump in some more alcohol to help rinse it out some more.

Here endeth the quote from ancient history.

happy coaching!
buswarrior

[belfert]

BW, Is alcohol really the right substance to use for this?  I thought someone said it is hard on seals and valves?  Won't I reduce my air capacity by filling the tanks with fluid?

I've been thinking about it and I'm wondering how the air dryer could have had so much moisture in it?  I know during normal operations I hear the purge valve let out a puff of air on a routine basis.  The bus was last driven on the road about 4 or 5 weeks ago when it was above freezing.  The previous owner was a charter operator that appears to be out of business.  (Bus may be a repo.)  They seem to have neglected the air system.  The bus was 11 years old when I got it and it appears I was the first person to ever have serviced the air dryer when I did that 3 or 4 years ago.

I didn't finish getting the air dryer serviced today as I can't get the dessicant cartridge loose with my strap wrench.  I have to take the old cartridge back as a core so I'll see if the parts place can get it off for me.

[buswarrior]

Yes, avoiding the use of alcohol in the air system is the preferred route, according to Bendix.

However, once the air system has been moistened, what choice do you have if you want it to work in the cold?

Never mind the loss of capacity for air due to some alcohol. Not significant versus the trade off of being functional. How do you know you aren't full of water behind those auto drains in the back?

The time for keeping the air system dry is 365 days a year, not after freeze up.

Too late for polite religious observances now... an exorcism is in your future...

If you are really pained by violating the coach with alcohol, in the summer, when this is all over, you may crack open the supply side of various valves (brake treadle, relay valves for rear axles) and give them a spray of your favorite good quality spray lube, one without a solvent in it, re-assemble and put it through its paces.

Get the air drier sorted out, dose the system with alcohol, get down to Arcadia, enjoy the coach during the cold weather, drain the rest of the tanks in the spring, keep the air drier and system in tip top operating condition from now on, never have a problem with freezing again.

happy coaching!
buswarrior

[stevet903]

Brian - how is your compressor discharge line routed?  From the Bendix compressor book:

The discharge line must maintain a constant slope down
from the compressor to the air dryer inlet fitting or reservoir
to avoid low points where ice may form and block the flow. If,
instead, ice blockages occur at the air dryer or reservoir
inlet, insulation may be added here, or if the inlet fitting is a
typical 90 degree fitting, it may be changed to a straight or
45 degree fitting. Shorter discharge line lengths or insulation
may be required in cold climates.

While not all compressors and charging systems are
equipped with a discharge line safety valve this component
is recommended. The discharge line safety valve is installed
in the cylinder head (Tu-Flo® 550/750) or close to the
compressor discharge port and protects against over
pressurizing the compressor in the event of a discharge line
freezeup.