AIR DRYER INOP- No power- source?

[Andrmorr]

Installed a new dryer from suprman since RRAD was kind enough to paint over everything including the blow off and openings on my old one. Did some pre-intall testing and could not get a voltage reading on the dryer power lead from the truck(with the switches on )...it was obvious at GL during the recovery that the dryer wasnt cycling and now the new one doesn't cycle either. The CTIS, tires, windshield wipers, horn etc all seem to work fine. The CTIS bleeds the extra pressure in the cab under the winch control, and if I hit the HWY button the system does a pressure dump somewhere in the back so all seems normal except the dryer doesn't dump...New dryer install troubleshoot page doesn't help and am working my way thru the TMs but thought I'd post this problem so anyone else noticing this can follow along...any info, tips or theory's accepted gratefully. Andrew

 

[Swamp Donkey]

The power source is for the heater on the air dryer. The governor operates the air dryer with a signal air line. The air dryer will still function without the heater.

 

[Andyrv6av8r]

Installed a new dryer from suprman since RRAD was kind enough to paint over everything including the blow off and openings on my old one. Did some pre-intall testing and could not get a voltage reading on the dryer power lead from the truck(with the switches on )...it was obvious at GL during the recovery that the dryer wasnt cycling and now the new one doesn't cycle either. The CTIS, tires, windshield wipers, horn etc all seem to work fine. The CTIS bleeds the extra pressure in the cab under the winch control, and if I hit the HWY button the system does a pressure dump somewhere in the back so all seems normal except the dryer doesn't dump...New dryer install troubleshoot page doesn't help and am working my way thru the TMs but thought I'd post this problem so anyone else noticing this can follow along...any info, tips or theory's accepted gratefully. Andrew

I'm no expert but I don't believe that the CTIS bleeds extra pressure in the cab; at least mine doesn't. What max pressure are you showing on your gauges?

 

[gimpyrobb]

The power source is for the heater on the air dryer. The governor operates the air dryer with a signal air line. The air dryer will still function without the heater.

This!

 

[Suprman]

There is a valve body in the cab for the ctis. Air comes into the ctis system thru this valve then out to the wheels. You will hear air sounds in the cab but no air should escape. If air is coming out of the valve body then it needs to be rebuilt. The air dryer is all mechanical. The air line from the governor to the compressor unloader also goes to the air dryer. When governed pressure is reached the air dryer expello valve vents collected moisture. What does your air pressure go up to? you want to see around 135psi on the gauges. They won't both be exactly the same.

 

[Andrmorr]

The power source is for the heater on the air dryer. The governor operates the air dryer with a signal air line. The air dryer will still function without the heater.

Yeah it's a two fold problem but I was trying to list all the symptoms...the pressure gauges stay between 110-120. The valve under the winch handle cycles on and off while the CTIS HWY light is flashing and sometimes hangs a little before it closes. I'm sure it needs cleaning/replacing but the heater voltage is also MIA. While changing the dryer, I cleaned all the fittings and sealed the threads with Teflon paste. There are no air leaks in the truck other than the CTIS valve inside. What would stop the signal from the governor? if the governor was stuck wouldn't it make way too much pressure or none at all? Gotta educate myself on Air Governors...Learning is about to commence...

 

[Suprman]

At 120 psi the ctis system will cut out to save air for truck use. You want to be around 135 and when driving the ctis will have all the air it needs. If your governor system is working but the air dryer is not expelling moisture after turning the governor up a bit, check the line going to the air dryer. It's the small line.

 

[Andrmorr]

At 120 psi the ctis system will cut out to save air for truck use. You want to be around 135 and when driving the ctis will have all the air it needs. If your governor system is working but the air dryer is not expelling moisture after turning the governor up a bit, check the line going to the air dryer. It's the small line.

That sounds like exactly what's happening! Thanks... Think I'm gonna replace the governor to make sure it's 100%, rebuild/repair the old one and have it as a spare...any recommendations on the best (latest) governor NSN, there seems to be several.
Still working on where to start for the heater power. I haven't found it in the TM's yet but am still reading...

 

[juanprado]

That sounds like exactly what's happening! Thanks... Think I'm gonna replace the governor to make sure it's 100%, rebuild/repair the old one and have it as a spare...any recommendations on the best (latest) governor NSN, there seems to be several.
Still working on where to start for the heater power. I haven't found it in the TM's yet but am still reading...

You have to use the 5 part 23 series for abs brakes. The older 24 does not have abs brakes since they were added later.
http://www.steelsoldiers.com/showthread.php?121487-TMs-for-M939-Series-Trucks

 

[Andrmorr]

You have to use the 5 part 23 series for abs brakes. The older 24 does not have abs brakes since they were added later.
http://www.steelsoldiers.com/showthread.php?121487-TMs-for-M939-Series-Trucks

That explains it...I did not realize the dryer was part of the ABS...thanks for the tip.

 

[Swamp Donkey]

Does your compressor ever cut out, or does it run continuously? If you never make it above 120 psi you're not reaching cut out pressure and this would cause the governor not to activate. This would then cause the dryer not to purge. It sure sounds to me like you have a leak somewhere.

While I don't have CTIS, and only have a general understanding of the intricacies of it, I'm with Superman. Get the main air system working correctly and that might take care of the CTIS issues. Trying to troubleshoot two systems at the same time when one completely relies on the other to work properly will result in much aggravation.

 

[Andrmorr]

Does your compressor ever cut out, or does it run continuously? If you never make it above 120 psi you're not reaching cut out pressure and this would cause the governor not to activate. This would then cause the dryer not to purge. It sure sounds to me like you have a leak somewhere.

While I don't have CTIS, and only have a general understanding of the intricacies of it, I'm with Superman. Get the main air system working correctly and that might take care of the CTIS issues. Trying to troubleshoot two systems at the same time when one completely relies on the other to work properly will result in much aggravation.

I definately agree...slow computer issue is really slowing me down on perusing the TMs...When I get back to the truck I'm going to look at the governor pressure setting first, check the control line for blockage, and why the pneumatic controller under the winch handles is cycling...I definately appreciate the different points of view...it keeps me from getting tunnel vision...

 

[Swamp Donkey]

Here's something else to bog down your computer. Some of this doesn't apply to our trucks but it's very helpful regardless. I'd take a close look at page 12...

View attachment Bendix Air System Troubleshooting Guide.pdf

 

[Andrmorr]

Here's something else to bog down your computer. Some of this doesn't apply to our trucks but it's very helpful regardless. I'd take a close look at page 12...

View attachment 541677

Thanks...that's definitely a handy TBLSHOOT guide...I wish diagnosing these trucks was as cut and dried as these guides make it sound! The TM's do the same thing...does it work YES/NO...if Yes put it back in service...If NO report it to your supervisor...doesn't work well for our civilian private ownership model though!