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Old 04-20-2012, 12:18 PM   #15
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Originally Posted by Skip426 View Post
I'll agree that Murphy is in the building ; and throw in my 2c worth. The dash on my coach gets all it's info from the VIM ( vehicle information module ) in the engine bay. Via a data link connection, a twisted pair of wires from the engine bay to the front of the coach. If the installer disturbed the VIM ground in the engine bay ; rear frame rail area; or hooked into the data link wiring by mistake , all the dash readings/warnings will be haywire. The power posts you discribe , should be 1 chassis batt power 2 coach batt power, a cross feed through the controller between the 2 can also give you problems.
Was your coach pre-wired , front to rear for the controller ?
Or did the installer run his own wiring to the trailer connector ?
If the installer had the trailer connector apart, look there first.
When it comes to wiring issues , I'd rather be lucky than good !
So Good Luck.
PS. I'm trying to find out why my fuel gauge reads a 1/4 tank high when my headlights are on, and not making any progress.
Contact Freightliner help line for wiring diagrams, have your serial # when you call. Join Access Freightliner, tons of good info there too.
Skip
First off I'm pre-electric ('96 Cummins 12v), no fancy ECM's or VIM's or whatever for me, so that's out. I did have a round 4 pin conn on the back of the moho, I don't know if it was factory or aftermarket, but's it's a pretty outdated form-factor these days so we stranded it and installed a new 7 pin round (which fits all my other toys). We stole the LH/RH/Brake wires from the old plug for the new 7 pin, then ran new wire for the electric brakes, batt connection/fuse and ground.

I'm heading over to the coach today to start troubleshooting, since I know I'm not that good I'm hoping to get lucky

Thanks for the tip on Access Freightliner, I'll check it out.
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Old 04-21-2012, 09:59 AM   #16
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Originally Posted by Skip426 View Post
I'll agree that Murphy is in the building ; and throw in my 2c worth.... When it comes to wiring issues , I'd rather be lucky than good !
So Good Luck.
Man, you have no idea.

Personaly, I would never recommend using the "track down electrical problems by following the smoke coming out of your dash" process, but sometimes you do get lucky. Yesterday while troubleshooting the low air problem I was idling the engine, watching my air guage NOT build pressure. Arghh... Well, the sun was getting hot sitting there so I flipped on the overhead cage fans to get some air moving and the switch literally fell apart, sparks flew and a lovely curl of smoke came up from under the dash. Yikes!

So after shutting 'er down I opened the access hatch on the top of the dash and found that the neutral and hot wires for the fan switch had melted together in about 5 places. Great. But while trying to pry loose the melted mess of what used to be switch wires I accidently moved the air supply tubes going to the park break, and one of them started hissing. Hmmmm... on further inspection there was a long slit on one of the lines just gushing air.

After a quick trip to Frieghtliner for a new ferrel (and fan switch) I cut out the offending section of air line and BAM - one air leak found and fixed. And as a bonus, once I got rid of the direct short my dash heater blower started working again. Yep, sometimes you have to be lucky. Never in a hundred years would I have thought to open the fuse cover on the dash to check for air leaks.

It didn't solve my air problem entirely, after a good 5 minutes of reving the engine I did get it up to about 75psi, better than the 45/50 I had before but nowhere close to where it should be. At least I can now drive the coach to the shop if necesarry.

Today I'm doing the under-coach crawl with a spray bottle of soapy water. If that doesn't reveal something obvious I'm not sure where to go from here.
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Old 04-21-2012, 10:59 AM   #17
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Crawl under with caution , as your suspension may drop
Air system charge time should be under 2 mins.
While your at it check the fuse size on your fan circuit ; it should have blown before the wiring got that bad.
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Old 04-21-2012, 11:17 AM   #18
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Besides repairing the issue find the noisy alarm device and wrap some electrical tape around the noise hole to reduce the screaming to a tolerable level.
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Old 04-21-2012, 02:57 PM   #19
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Besides repairing the issue find the noisy alarm device and wrap some electrical tape around the noise hole to reduce the screaming to a tolerable level.
That's funny. I actually did try to find the screecher devise, I'm sick of listening to it. I think they hid a trained banshee somewhere in the dash, the noise seems to come from everywhere. I couldn't find the little bugger .

But it looks like I've lost the battle anyway. Got to the coach this morning and it was still sitting at about 70psi, same as last night. So it isn't leaking air, it just won't pressurize any higher. Checked every line and fitting I could find and nothing, zero nada, zip. So it must be the compressor itself or one of the 752 valves, controllers, diverters, whatever, that are bolted all over the moho.

I hate giving up but don't know where to go from here. I suppose I could buy an air guage and a bunch of fittings and check the pressure on both sides of every line on the coach until I find a drop, but I'd likely end up with more leaks than I have now (16 year old fitting hate to be disturbed). So unless someone else has a brainstorm I may just have to pay for this one
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Old 04-21-2012, 03:48 PM   #20
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Ok, so it appears you have no leaks past the tanks; one way check valve in the supply line at the tanks. That narrows it down considerably. You have to trace the air line from the compressor to the dryer and up to the holding tanks. The problem my be the water purge port solinoid on the bottom of the air dryer not fully seating ; if it was wide open you would not build up any air. This is where it gets tricky & a little dangerous. You have to get to the dryer when the engine is running to check it . Block the coach up , or have the stabilizers down, before getting under the unit. The unit I worked on with this problem ; no build of air; the valve was wide open. The valve was held to the bottom of the dryer with 3 , 10mm head size bolts, there was another bolt dead center of the valve that we did not have to remove. Pushing on the center bolt sealed up the leak and the unit built up air , but the fix was removal of the valve for cleaning. If this is your leak, and you remove the valve yourself; bleed all the air out of the system first;disconnect the 12v power wires, remove the mount bolts and pull the valve straight out; turning it will cut the "O" rings, clean the valve with brake cleaner spray, lightly coat the "O" rings with approved lube, and push straight in to the dryer. If necessary to transport the unit to a shop for repairs you can by-pass the dryer , just hook the in/out air lines together for the trip.The boys at Freightliner help line can give you more info, also there are downloads on dryer maintenance on their web page.
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Old 04-21-2012, 03:56 PM   #21
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Besides repairing the issue find the noisy alarm device and wrap some electrical tape around the noise hole to reduce the screaming to a tolerable level.
The main reason the buzzer is hidden is to prevent you from doing this, the warning is to give you enough time to get to the side of the road before the rear brakes lock up due to low air, so it has to be loud enough to be heard over road/engine /radio and DW noise .
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Old 04-21-2012, 07:23 PM   #22
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Ok, so it appears you have no leaks past the tanks; one way check valve in the supply line at the tanks. That narrows it down considerably. You have to trace the air line from the compressor to the dryer and up to the holding tanks. The problem my be the water purge port solinoid on the bottom of the air dryer not fully seating ; if it was wide open you would not build up any air. This is where it gets tricky & a little dangerous. You have to get to the dryer when the engine is running to check it . Block the coach up , or have the stabilizers down, before getting under the unit. The unit I worked on with this problem ; no build of air; the valve was wide open. The valve was held to the bottom of the dryer with 3 , 10mm head size bolts, there was another bolt dead center of the valve that we did not have to remove. Pushing on the center bolt sealed up the leak and the unit built up air , but the fix was removal of the valve for cleaning. If this is your leak, and you remove the valve yourself; bleed all the air out of the system first;disconnect the 12v power wires, remove the mount bolts and pull the valve straight out; turning it will cut the "O" rings, clean the valve with brake cleaner spray, lightly coat the "O" rings with approved lube, and push straight in to the dryer. If necessary to transport the unit to a shop for repairs you can by-pass the dryer , just hook the in/out air lines together for the trip.The boys at Freightliner help line can give you more info, also there are downloads on dryer maintenance on their web page.
Thanks for the help Skip, I really don't want to visit the hospital, Freightliner is mighty proud of the labor rates

So to be clear, to troubleshoot I remove the three #10s holding the solinoid and then with the engine running I push up on the center bolt? And if by pushing on the center bolt I begin building pressure - BINGO?

I have two lines coming off the compressor, one quite large, maybe an inch or 1 1/4" dia, the other smaller, maybe 3/4 or 7/8. The larger of the two disappears towards the front of the coach. I can't really trace this one, once it disappears - its gone. I have no idea where it pops back out at. The smaller of the two routes straight to what I believe is the dryer. If I have the right component in mind for the dryer I can access it through the rear PS basement door, no underside work required.

I'll give it another look tomorrow, I'm toast for today. Oh, BTW while dinking around under the dash fixing the fried wires I discovered the main plug for the heater controls was disconnected, just hanging there. Plugged it back in and low and behold I have a three speed fan again, even high speed now kicks in. Will wonders never cease
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Old 04-21-2012, 07:37 PM   #23
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When was the last time you replaced the air dryer cartridge, also ,how about the purge valve.
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Old 04-21-2012, 07:54 PM   #24
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When was the last time you replaced the air dryer cartridge, also ,how about the purge valve.
I just had a full service done a few weeks back, and although I told them specifically to change every filter they could find, I can't say with certainty they hit the dryer. And I doubt seriously if the valve itself has ever been changed.
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Old 04-22-2012, 09:52 AM   #25
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There is also an air compressor regulator located on the compressor. I am aware of a couple of these failures. In that case, the symptoms you are describing have occurred.

Here is a copy from another web site that describes the way to change it.

Jim


AIR COMPRESSOR GOVERNOR



Webmaster Note - I recently had a problem with my air. On initial startup, the air would not build up above 70 psi, and would fall rapidly with application of the air horn or air brakes. Sometimes, dumping the air and restarting would restore normal operation. FL San Antonio diagnosed this as a faulty air compressor, but based on John's article, I think it was probably just the governor. Based on John's experience with two failed governors, I now carry a spare governor. Thanks to John for this excellent article. John has also provided the excellent pictures along with his article. Click on a thumbnail for a larger view.

The air governor is located on the rear of the air pump on the curb side of the engine up next to the front (rear of the coach. Note the belt pulleys, etc). It is mounted on the pump with two bolts that need an allen wrench to remove them. Also, there are two small air lines running to the governor that will have to be removed (don't get the air lines crossed).

VERY IMPORTANT!To change the governor, first and foremost, completely bleed the air from the system by pumping on the brake pedal until there is no pressure on the guages.

Remove the air lines from the governor and don't get them mixed up (you may want to tag them). Remove the two screws with an allen wrench and remove the air governor. Here is a picture of a new governor.

On the outside where you have more room, examine the governor and remove the two fittings that go to the air lines and place them on the new governor. Remove the plugs on the old governor and install on the new governor, insuring that they are installed exactly as they came out of the old governor. Proir to installing the plugs, use teflon tape or other sealer to create a tight seal. Also put teflon tape or other sealer on the air line fittings. Once you are ready to reinstall the governor, place the gasket (supplied with the new governor) and screws on the governor and bolt in place. Reinstall the air lines and you're ready to go!!!

Most of the above is self-explanatory, once you see the governor and recognize what it does.

The governor is adjustable as to air pressure on the system, as shown in this photo. The screw will adjust the air pressure up or down. I had approx 130 lbs showing on my guages when the governor went out.
Part Number for the governor: Bendix 275491, which you can pick up at any large truck facility.
Doing this the other week saved me from a tow and a long wait at wherever I would have to had it fixed!!
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Old 04-22-2012, 10:42 AM   #26
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Jim wrote "On initial startup, the air would not build up above 70 psi, and would fall rapidly with application of the air horn or air brakes. Sometimes, dumping the air and restarting would restore normal operation."

Hmmm... sounds almost exactly like what I am experiencing.

When the original poster referred to "dumping air", did that mean dumping the entire system via the purge valves on the tanks plus dumping the bags, pumping the brakes, etc. or just dumping the bags through the leveling jack system? I've dumped the bags a couple of times now which didn't seem to change anything.

I do kind of like this idea. I just don't believe its the compressor, there's some sticky or plugged or tired or whatever component between the compressor and the tanks that's stuck at precisely 70psi and I'm beginning to wonder if a clogged dryer filter or hung purge valve would result in passing the exact same pressure every time I cycle the system. It's almost like my 70psi is being "regulated," which I suppose is what a regulator is meant to do, albeit in this case at a much higher setting :-)

Thanks for the info Jim, I do appreciate it.
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Old 04-22-2012, 11:51 AM   #27
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Quote:
Originally Posted by jlfbatonrg View Post
There is also an air compressor regulator located on the compressor. I am aware of a couple of these failures. In that case, the symptoms you are describing have occurred.

Here is a copy from another web site that describes the way to change it.

Jim


AIR COMPRESSOR GOVERNOR



Webmaster Note - I recently had a problem with my air. On initial startup, the air would not build up above 70 psi, and would fall rapidly with application of the air horn or air brakes. Sometimes, dumping the air and restarting would restore normal operation. FL San Antonio diagnosed this as a faulty air compressor, but based on John's article, I think it was probably just the governor. Based on John's experience with two failed governors, I now carry a spare governor. Thanks to John for this excellent article. John has also provided the excellent pictures along with his article. Click on a thumbnail for a larger view.

The air governor is located on the rear of the air pump on the curb side of the engine up next to the front (rear of the coach. Note the belt pulleys, etc). It is mounted on the pump with two bolts that need an allen wrench to remove them. Also, there are two small air lines running to the governor that will have to be removed (don't get the air lines crossed).

VERY IMPORTANT!To change the governor, first and foremost, completely bleed the air from the system by pumping on the brake pedal until there is no pressure on the guages.

Remove the air lines from the governor and don't get them mixed up (you may want to tag them). Remove the two screws with an allen wrench and remove the air governor. Here is a picture of a new governor.

On the outside where you have more room, examine the governor and remove the two fittings that go to the air lines and place them on the new governor. Remove the plugs on the old governor and install on the new governor, insuring that they are installed exactly as they came out of the old governor. Proir to installing the plugs, use teflon tape or other sealer to create a tight seal. Also put teflon tape or other sealer on the air line fittings. Once you are ready to reinstall the governor, place the gasket (supplied with the new governor) and screws on the governor and bolt in place. Reinstall the air lines and you're ready to go!!!

Most of the above is self-explanatory, once you see the governor and recognize what it does.

The governor is adjustable as to air pressure on the system, as shown in this photo. The screw will adjust the air pressure up or down. I had approx 130 lbs showing on my guages when the governor went out.
Part Number for the governor: Bendix 275491, which you can pick up at any large truck facility.
Doing this the other week saved me from a tow and a long wait at wherever I would have to had it fixed!!
I agree with jlfbatonrg. My very first thought when I began reading this thread was that you had a bad air governor. That is what the symptoms you describe suggest.
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Old 04-22-2012, 11:54 AM   #28
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I just had a full service done a few weeks back, and although I told them specifically to change every filter they could find, I can't say with certainty they hit the dryer. And I doubt seriously if the valve itself has ever been changed.
If the dryer filter was replaced, the shop may have inadvertantly left the filter/filter housing loose, or allowed a speck of dirt into the purge valve, thats alowing a leak. Check your invoice from the shop and see what filters you were charged for. Then if you feel comfortable going under the coach with the engine running , listen for any leaks in the area of the dryer. Eye protection & gloves please. If you leak is from the purge vavle , then pull it off the dryer and clean it . Some dryers have a spin on filter, similar to a large oil filter , and if your leaking at the filter gasket ,then remove the filter and clean the gasket/ mateing surface , lube and re-install. Other types of dryers have a can filter housing, held down by 4 bolts. Drain all the air at the tanks before working on any air system part.
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