MCI 102c3 6v92ta Mechanical Won't Air Up

[Jcparmley]

Hello All

My bus has been sitting for a year due to a air dryer leak.  So I replaced the air dryer with a new unit and started the bus.  The bus didn't build up any air pressure.  The gauge shows now air pressure, and the brake pedal is dead.  There is no air leaking sound so I don't think it is an air leak.  Do you think it is the compressor?  Is there something I can check on the compressor such as a valve, etc?

[chessie4905]

did you disconnect the proper air line connections? disconnect output from air compressor and see if it is producing air. could be the governor if getting air or compressor if not.

[Jcparmley]

The governor inside the air dryer?  The air dryer is brand new.  I guess that doesn't mean much anymore.

Good suggestion about removing the air line at the compressor and see if it's pumping air.

did you disconnect the proper air line connections? disconnect output from air compressor and see if it is producing air. could be the governor if getting air or compressor if not.

[chessie4905]

Governor attached to air compressor. 1 1/2 round x about 4"

[Jcparmley]

Oh, ok.  Thanks.  I will check the governor. 

Governor attached to air compressor. 1 1/2 round x about 4"

[Coach_and_Crown_Guy]

I'm not sure I remember it all correctly, but I have the impression that there is a communicating air signal line between the air governor and the compressor head actuating valves in the head. This line is how the air governor turns the compressor on and off. There's also another air signal line to the air dryer (AD9?) that actuates the spitter valve on the bottom to purge the collected moisture every time the air governor cycles the compressor. I suspect any number of possibilities of these various communication air signal lines may not be connected as they should be, (or even connected at all). Find and check out tech support online the easily available Bendix Air systems connection diagrams and you should be able to track it down. The Compressor not putting out could be as simple as the actuating, (unloader), valves not being enabled. Not actually a failure of the compressor. I would think any competent mechanic who works on heavy duty air systems would be able to help you troubleshoot and resolve this issue.

[Jcparmley]

I drove out the the shop and started the bus.  I couldn't get the line off the back of the compressor because I didn't have a big enough wrench with me.  However, I did open the valve on the passenger rear engine hatch just above the rear air tank and it was pumping air.  So my guess it has something to do with getting the air to or out of the new air dryer.  Is there some sort of valve I need to open on the new air dryer? 

did you disconnect the proper air line connections? disconnect output from air compressor and see if it is producing air. could be the governor if getting air or compressor if not.

[buswarrior]

Signal line to the air drier is missing/corrupt.

The air drier is a giant plug, if it is in the purge mode.

Air compressor governor gets an air preesure signal from a tank via a small line, and a small line goes from the governor to the air drier to coordinate the changes.

Happy coaching!
Buswarrior

[Jcparmley]

The signal wire is a single wire.  The air dryer plug had two wires.  One was obviously for the signal wire the other was I assumed ground.  Neither wire was identified so I made a guess.  Could that be the issue? 

Signal line to the air drier is missing/corrupt.

The air drier is a giant plug, if it is in the purge mode.

Air compressor governor gets an air preesure signal from a tank via a small line, and a small line goes from the governor to the air drier to coordinate the changes.

Happy coaching!
Buswarrior

[Jcparmley]

So if the air compressor governor is bad would I still be able to feel the air from the rear engine compartment air bleed valve.  I use that port to connect an separate air compressor in order to fill the bags without running the engine. 

The signal wire is a single wire.  The air dryer plug had two wires.  One was obviously for the signal wire the other was I assumed ground.  Neither wire was identified so I made a guess.  Could that be the issue?

[dtcerrato]

I'm no expert but get by plenty good. I wouldn't think it a good idea to tap anywhere on the main engine compressor governor with an aux. compressor tap. My preference is the discharge muffler area to tap the aux. electric back up air compressor and even there will effect the governor's normal cycles but the aux. air still has to pass through the drier which is a good aim. Just sharing my thougjts.

[chessie4905]

wires for air drier should only be for the heater. rest should be tw normal sized airlines and a signal line connecting into correct port on governor. Did the new drier com with a manual for installation? If a Bendix, many places to Google on its operation and trouble shooting.

[Jcparmley]

So we think it might be the governor on the compressor?  So please help me understand.  If the governor was bad would the valve (in the engine compartment where it says to drain daily) have air? I would think if the governor was not working properly there would be no air in the system at all.  Or am I missing something. 

wires for air drier should only be for the heater. rest should be tw normal sized airlines and a signal line connecting into correct port on governor. Did the new drier com with a manual for installation? If a Bendix, many places to Google on its operation and trouble shooting.

[Van]

Do you have the two smaller lines going to the governor mixed up?

[chessie4905]

all ports on governor are marked. some are plugged.

https://www.sgi.sk.ca/air-brake/-/knowledge_base/air-brake/air-governor