Any ideas for fixing cold weather problems with air compressor?

[belfert]

I have a Bendix Tu-Flo 750 compressor on a Series 60 with a D2 governor (pretty standard stuff).  It will not compress air when it is below freezing.  It has never compressed air properly at below 32 degrees, but has worked fine at higher temps.  There is what sounds like air loudly purging about every five seconds from the compressor.

The air dryer dessicant and purge valve were replaced 15,000 miles ago, rear tanks have auto drains, and the front tanks have been drained regularly.  None of this should matter as this stuff is all after the compressor.

I was told by someone to replace the D2 governor to fix this issue.  I did so and I am getting the same exact issue as before.  I do hear an air leak from the compressor after the engine is off, but not sure if that was an problem before.

Where do I go from here?  Still a governor issue or something else like a bad compressor or bad unloader valves?

[belfert]

I talked to someone about my issue and he said it is not the governor and is almost certainly a moisture/ice issue.  It was explained that the unloader valves are purging air because the air being compressed has nowhere to go and the unloader valves will expel the air at 200 PSI for safety reasons.

Should I be unhooking the line from the compressor to the air dryer at the dryer to see if air is moving there?  I would think the blockage has to be pretty close to the compressor to not let any air into the system at all.

[robertglines1]

as suggested air line heat will remove moisture from lines:sometimes referred to as air line antifreeze/ air compressor head bolts should be torqued to 440   to    500  inch lbs. to get ft lbs divide by 12 . take discharge line off air compressor and dump in then reattach.Is your dryer working?

[luvrbus]

Make sure the intake is clean if yours has a separate air cleaner for compressor change it and be sure the auto drains are working properly they give problems in cold weather


good luck

[belfert]

Isn't any sort of chemical to remove moisture/ice from air lines a no-no when the purge valve on the air dryer has a heater?

I'll have to check if the heater on the purge valve seems to be working.

[Tony LEE]

This topic reappears every year and I don't recall any warnings - possibly because heaters in the dryer are pretty standard. Some buses have special antifreeze delivery systems permanently installed.

[belfert]

This topic reappears every year and I don't recall any warnings - possibly because heaters in the dryer are pretty standard. Some buses have special antifreeze delivery systems permanently installed.

Aren't the buses that had airline antifreeze delivery systems generally older models without air dryers?

[bevans6]

All sorts of vehicles have air line antifreeze systems including modern ones, the point is that the air line antifreeze is introduced into the wet tank or some other location which is after the air dryer.  The air line antifreeze is harmful to the desiccant in the air dryer, so it should not be introduced before the air dryer.

There are probably older installs before air dryers were common where the antifreeze was introduced right after the compressor, in which case they should probably be  disabled or moved if an air dryer is retrofitted.

This sounds to me like the intake, discharge or unloader valves sticking.  The air compressor continually compresses air, the unloader valve diverts it to atmosphere when told to by the governor.  My manual says the unloader needs to be lubricated with a special lube, dimethyl polysiloxane, http://en.wikipedia.org/wiki/Polydimethylsiloxane

It will apparently lube your unloader, keep your hair shiny, and make your Chicken McNuggets tasty and crispy.  I kid you not, the things you learn on a Friday morning on the Bus Forum...

Anyway, I think you need to service your compressor.

Brian

[buswarrior]

Do you have power to the heater on the air drier?

It matters a whole lot in the cold.

happy coaching!
buswarrior

[robertglines1]

just thought of easy ck to see if it is compressor or air system blockage.  Make you a adapter and either put shop air to the air system Thur air compressor discharge/delivery hose  or  discharge( from air compressor) into a separate portable tank with a gauge on it if you don't have shop air.   would let you know where problem is for sure

[belfert]

Do you have power to the heater on the air drier?

That is one of the first things I plan to check today when I go out to look at things again a little later.  We got 6 inches of snow overnight which will slow things down a bit.  If I have power how do I know if the heater element is really working?  Will it be warm to the touch?

[buswarrior]

Heater has a certain resistance. Check the Bendix manual for the number and use your ohm meter settings on the mulit-meter to confirm continuity and the proper resistance.

happy coaching!
buswarrior

[belfert]

I found part of the problem.  I assumed the air dryer is 24 volt so I installed a reman 24 volt purge valve.  Well, when I tested the voltage today it only showed 12 volts.  I double checked the wiring diagram and sure enough, the air dryer is 12 volt.

I found a place still open today where I can get a replacement purge valve.  I'm not convinced this is my only problem yet.

[robertglines1]

Brian good catch! it's the simple ones that seem to get buy us. fingers crossed that's it    Bob

[belfert]

A 24 volt purge valve is $90 at one place and $105 at C&J Bus Repair.  A 12 volt version is only $50 on sale!  I suppose they make a lot more of the 12 volt version.  I hope they will take the 24 volt as a core.

A fair bit of moisture came out of the air dryer when I pulled the purge valve.  I had tried to heat the purge valve, but maybe not long enough.  I think I'm going to spend the $21 and replace the dessicant cartridge even though Dina made taking out the air dryer a 2 hour project.  The space they choose isn't wide enough to get the wrench in easily to disconnect the lines.