I could use some forum wisdom here... I was coming down the mountain from Idyllwild and got the air loe air pressure alarm. After pulling over and checking things over, I used the aux compressor to raise the coach (which adds air to the front and rear tanks and got further down the mountain where I pulled over once again. Checking things over, I tapped the D2 with small hammer and didn't notice any difference, but after using the aux compressor to add air, I started down the road again, lo and behold it once again behaved normally building pressure to cut out and and cutting back in as usual. This continued until I got to our home base (about 60 some miles) until I was pulling into our site whereupon it stope building air. Since the only thing I did at the second stop that might of affected the air system was to tap on the D2 governor, I had high hopes that changing the D2 would fix it. Sadly, it did not. I need to move it from our site down to the storage lot (less than a quarter of a mile from our site) and so will try bypassing the air dryer tomorrow. Before when I was stuck by the side of the road in Canada, the air dryer had failed and the air was continuously puking out of the p-urge valve on the bottom of the air dryer, that is not happening now... I would appreciate some speculation or better yet, likely approaches to a solution before I tackle the issue again tomorrow.
Don
The D2 governor does two things. It signals the air dyer to purge and it lifts the valves in the air compressor to stop the pumping action. If the valves won't return to service, you won't have air. Think stuck.
I'm thinking along the same direction as Old Toolmaker.
There's really only 3 components involved in the air pressure "generation" process: the engine air compressor, the D2, and the air dryer. Since your malfunction is intermittent (randomly comes and goes) it is obviously not a blocked or blown out air hose. You changed out the D2 so we may assume it is OK. You are only too familiar with air dryer failure symptoms, and have ruled that out. Only thing left is the air compressor.
I thought you installed the ARB 12V air compressor so you could pressure up the air system with it? Use it to make the drive to storage lot?
Bypassing the air dryer (my next step as well as hopefully aiding my move down to storage) should tell me if the compressor is doing its thing or not... likely a stuck valve in the air compressor if it doesn't. I did spray a bit of WD40 in the unloader port of the D2 mount, maybe it will free up something. R&R of the air compressor is not something I look forward to...
Don
As it is right now, the aux is only triggered by the leveling system. I have yet to wire in the switch to control it directly. It will work to get me down to storage if I raise it up as high as I can and then let it settle to ride height.
Don
Don I'm unfamiliar with our air compressors but on other compressors reed valves are used. I have seen them have one of the mount screws back out and rotate so as not to seal. Also seen them fatigue crack. I'm very curious to your findings. I'm sure some type of unloading valve is used, but have no clue. Suspect a affordable repair if the compressor is not damaged. Your bypass fitting will give good indications
Scott
I have had the unloader valves stick on my crane. It uses a Bendix compressor. I was able to spray Corrosion X into the head assy. by removing 2 bolts and fixing the problem. The valves on it are like an automobile engine and the valve stems were sticking. I don't knows how the one on my Cummings engine works but if it has a similar configuration the same thing could happen and maybe the same cure would work.
Don,
If the dryer checks out OK then here are some thoughts on the compressor and D2.
If the compressor pumped any at all that leads me to believe that it (the compressor) is just fine. Now that don't mean that you don't have trouble with the unloader which is a bolt on part. Depending on which compressor you have will depend on what type valves and unloader you have. So crawl up in there and get a picture of the model Hoslet (WAG here) compressor you have. There are unloader rebuild kits out there and most are ~$50. You can use Kroil also and do like Cman suggest by spraying into the compressor inlet/unloader and see if it can loosen up some gunk that can build up in there. If you do have to pull the unloader it can be done on the coach which will save you some extra work. One word of caution is if you do pull the compressor some have to be timed with the engine (here in lies the extra work from above) so read up on timing before you start.
Now I know this may seem like a remark from an over educated burro (smart azz) but when you replaced the D2 did you make sure that you had the plugs in the right ports? Or it could be a bad rebuilt D2 so try another one before you tear into the compressor.
Mike
Can't help with fixing the problem but could you use your generator and an air compressor plugged into the external connection to keep it aired up to move it?
An electric compressor will not have the CFM to operate the brakes safely.
The generator will be able to drive a big enough air compressor to do the job.
I was slammed with sticker shock when I looked for an air compressor for my 8.3.. If I had been home I would have tackled rebuilding my on in my shop. Your lucky your home Don and not in El Paso Tx.
Scott sit back and think for a moment. The compressor is gear driven and turns anytime the engine turns, and it has poppet valves. All you need to do is lift the exhaust valve to stop the useful pumping of air. That's what the unloader mechanism does. It holds the valve open and the compressor goes wiffle wiffle wiffle.
If the unloader is coming and going a spritz of your favorite penetrating oil will buy you a little more time. Prudence dictates purchasing the kit, cleaning the unloader and replacing the wear parts.
For industrial air compressors 5HP is the dividing line. If your compressor doesn't cycle all that often you can start and stop the compressor. When you get into the other 50% of pumping capacity you change the compressor over to run all the time and use the unloader. The electric motor will thank you.
And yes some compressors use reed valves. It's just that these don't.
Thanks for the thoughts Mike... Our coach has a Holset compressor (which is bthe reason it has to have the external isolation valve on the air dryer). I see that find it parts may have a rebuilt unloader assy for about $75. I will have to remove items like the air dryer and my Davco primary fuel filter, but it may be changeable without removing the compressor... I will order one jsut to have if I can figure out the right part number. They also have unloader rebuild kits but the for less than a $100, it is a no brainer to to get the who;e assembly. I will remove the unloader plug from the D2 and try spraying some Corrosion X in the port. BTW, should the motor be running when I do this? Would it get drawn in or blown out? ::)
The compressor model is a Holset QE296EC
Don
Vet10 latest finditparts discount i have. May expire at 1158 pm today.
Mark
Not sure whether or not these are direct replacements for the Holset model I have, but a search on "Holset QE296EC
" yields 3558072X by HALDEX - Remanufactured Cummins/Holset Style Compressor - QE296 (http://www.finditparts.com/products/1681560/haldex-3558072x#description)
Note that it lists just the QE296 without the suffix EC. I don't know what the letters "EC" refers to, but it may be significant, i.e., port orientation, the fact that it doesn't include the unloader assy, or?
In any case, the price for a rebuilt at less than $300 (plus a $312 core charge) plus a rebuilt unloader assy @ <$50? Speaking of the unloader assy, anyone know how I can tell if this is the right one for my compressor?
3559582X by HALDEX - Remanufactured Compressor Unloader Assembly (http://www.finditparts.com/products/1561700/haldex-3559582x)
Sounds like a fairly reasonable price to me, but first I would by the unloader assy and try it if the compressor doesn't build air after I try bypassing the dryer...
Don
Found one that has similar "assembly number" (plus the "X") to the metal tag in your photo:
Cummins/Holset Compressor - 3558186X/QE296 (https://powerbrakes.com/3558186x-qe296-cummins-holset-compressor/)
If you look at the different QE296 compressors in the link below, you can see 3 different mounting flange configurations. The "EC" suffix on your compressor's model number might refer to mounting flange type?
Holset / Cummins QE296 Compressors (https://powerbrakes.com/air-compressor/holset-cummins-air-compressor/qe296/)
Catalog link below, see page 1-38, top left diagram for Assembly Number 3558186:
http://precisionrebuilders.com/pdf_catalogs/AirCatalogPAB-0902.pdf
The compressor you linked (above) says it is for Cummins L10/N14 engines. Not what you got (different mounting flange).
The one below says it is for Cummins C-Series. Also note the correct Assembly Number.
3558186X by HALDEX - Remanufactured Cummins/Holset Style Compressor - C-Series (https://www.finditparts.com/products/1681571/haldex-3558186x?sctx=eyJzIjoiMzU1ODE4NiIsInNvdXJjZSI6ImF1dG9zdWdnZXN0IiwicHJvZHVj%0AdF9pZCI6MTY4MTU3MSwicmVzdWx0X2NvdW50IjozLCJyZXN1bHRfaWR4Ijow%0AfQ%3D%3D%0A)
Thanks for the research Chuck! ^.^d I want to get a rebuilt unloader assy but the one that is suggested at Find It Parts is shown as not available. This part looks like it should be used across many models. I wonder how universal they are... I would like to have one assembled in hand so I can drop~n~swap if possible, but as yet I find none for direct sale from a website. If I can find a rebuilt to buy, I plan to take the old one apart and maybe fix, so I would just eat the core charge.
Don
That would be my approach as well.
Richard
Update and some head scratching :o I got the coach down to our boondocking location safely. The head scratching is because bypassing the air dryer did not result in the compressor doing its thing. So... I add air with my trusty HF ultra quite compressor, and put (eventually ::) ) 120psi in. With the air dryer in the system, the wet tank would leak down while the brake tanks would stay at 120psi. But now with it bypassed, the wet tank stayed at 120! So, though it seem that the compressor is not compressing (I think it has to be a stuck unloader because of the fact that it started working normally long enough for me to about 65 miles of moderate elevation changes and winding roads and then failed again after stoping to unhook the towed here at home base. My reading on this is that the dryer has failed and the unloader valve has become stuck... maybe because of cr@p from the failed dryer??? What think you? I am going to pull the air dryer off and see just how hard it is going to be to get the unloader assy off. I have a brand new old stock one (along with a new isolation valve). I just have to fabricate a mount for it. I am going to see if I can work out a mount that will give me full access for servicing dryer from behind and better access to the compressor etc. The current mounting system is very inconvenient.
Don
Don,
Here is the part numbers that should fit the QE296 unloader. PAI # 220038 or Cummins 3803766. Make sure that you don't get a kit for the SS models as they won't work on the QE compressor. Here is a video of what you are up against. https://www.youtube.com/watch?v=9VM3m0dROV0
Mike
Pamela & Mike, that is an excellent video! Another video that makes it clear what type of air dryer Is applicable to the QE compressors used mostly before the 2000 model year, apparently only on the ISC powered model coaches.
http://www.youtube.com/watch?v=LjWQStJxXf8
Don,
What a lot of people don't understand is the need to use the correct air dryer that is mated to the compressor you have. Very good explanation in that video.
Mike
I have a new PURest air dryer that says it isn't compatible with Holset compressors. Without the isolation valve, I don't think the OEM "Pure Air Plus" is either. My thinking that the addition of an isolation valve See picture below) would do the same thing for the PURest that I have on hand... Any thoughts? I would consider that Turbo 2000 with the QE compatible configuration mentioned at the end of the short video I posted, but sounds like it might be pricy considering I can't find out how much they are without calling a dealer...
Don
We chased this issue down my coach in the spring. We did it is steps trying to find the problem... replaced the D2, no improvement. serviced the air dryer, slight improvement. Eventually replaced the engine compressor, which fixed the issue.
Don,
1. Correct, it will work somewhat but not properly
2. Correct
3. You are on a role, with out the isolation valve you will run the risk of pumping oil and this will cause carbon build up in the compressor and or unloader rendering your wallet grief.
4. About $450 (the last time I checked) this is made more like the AD-9 dryers in they are a lot easer to change out elements and clean the inner works. The replacement cartridge is about $50. The unloader and service kits are about $100 for both together (not each). So if you have an old style Pure air plus and need to service it, then replacing it with one of the Turbo 2000 (not to be confused with the turbo turd 3000) isn't that much more.
Mike
Don, we have the Pure Air Dryer but no Isolation Valve and it works fine.
Johnh
You have a different compressor (Wabco?) that doesn't need it. I think the 2000 model year is when that changed for the ISC powered coaches. Lucky you! :D
Don
Here is another video that sheds some light on the Cummins/Holset compressor/Air Dryer compatibility requirements.
http://youtu.be/EAZJuaX1xNM
I have ordered an SKF Air dryer from Find it Parts.
620500 by SKF - Air Dryer Parts (http://www.finditparts.com/products/203972/cr-slash-skf-620500)
There are several versions of this unit. The ones for Holset compressors have SKF part numbers that start with 620 and end in the 500's, i.e.; SKF 620500 Assy with bracket and external purge tank and various installing bits. Part number SKF 620502 is the dryer itself (and maybe the mounting bracket). SKF part numbers that end in the 600's (i.e.; SKF 620602 is the dryer unit only without the internal plumbing that the Holset compressor's need to keep the pump from passing oil. In my opinion, the Isolation valve required for the Holset compressor used with Pure Air Plus 3-line dryers used on the 1st year of the ISC's production is a is a band aid to make up for a design flaw.
Here is text from SKF's website that describes the model number nomenclature;
Since I hate the location of the OEM Haldex Pure Air Plus, the narrower profile of the SKF unit will allow me to make the air dryer much easier to service as well as simplifying the plumbing a bit. I am hoping to get it by Friday and will figure out the mounting details then. In the mean time, I am going to temporarily mount the Haldex PURest air dryer so I can diagnose the compressor issue, which due to the intermittent nature, is likely a stuck unloader valve.
Don
What gave it away? Maybe the "We need to keep the compressor under pressure or it pumps oil."?
I recently went through the same problem of suddenly not being able to build air. Cummins has a procedure to try and free up the unloaded valves in the compressor head. Since there is no external access to the valves without draining antifreeze and removing it. They suggest removing both the air intake hose and the main discharge line and spraying a Liberal amount of wd40 or penetrating oil into both openings and let it sit for an hour.I would run it prior to at least warm it up . After it sits ,start it up with lines off to let the yuck blow out. Carbon build up on the unloaded valves is a known problem, not so much on older non emissions engines. Tapping on the head with a hammer can help the loosening process. Reconnect the lines and hope for the best. The heads are available rebuilt or kits are available to do it yourself.
I saw you bypassed the Air dryer which is usually the most common problem of little or no air. You might want to rebuild the dryer while your in there if it hasn't been done in the last 2 years.
I received the SKF Turbo 2000 on Thursday after ordering it on Monday... excellent service from Find It Parts! The sales rep took the trouble to call SKF to check that parts shown in the picture on Find It Parts' website were all included on the part number I ordered. I reused the heavy duty bracket Foretravel made but hung it from the heavy frame that the motor mount carriage is attached to. The Foretravel made bracket, was sitting on the crossmember that supports the rear engine mount, is like a large piece of ¼" thick angle iron with a triangular gusset bracing added. Hanging it from the frame rail changed the orientation 180º. Since the SKF unit comes with a bracket that orients the I/O ports a 180º from the way the OEM Haldex Pure Air Plus was mounted, that worked out perfectly. After determining the exact position the bracket needed to be in, I drilled and tapped holes for ⅜-16 bolts which I screwed in from the back, making them in function as studs, That makes removing and installing the SKF unit much easier to install since I can just hang it from the studs. It opens up the area a bit and the the whole SKF unit (or just the spin on canister can be removed from behind instead of having to go underneath or removing anything else. Access to the D2 governor plumbing connections to the air dryer is improved considerably because the smaller overall diameter of the SKF unit VS the Haldex gives increased clearance from the engine. I have successfully got the unloader valve unstuck to prove that the compressor itself functions as normal, but it stuck again. Today I will undo the air intake for the compressor and WD40 the heck out of it from above.
Does anyone know whether or not coolant runs through the unloader valve housing? I don't see why it would be, but if so, I would rather remove and rebuild or replace the unloader assy when I am going to change the coolant anyway.
Just looking at the videos linked above again, I don't see any coolant passages in the unloader housing, so it appears the answer is no...
Don
Don,
You are correct there is no coolant in the unloader housing.
Mike
Confusing to me.. I ordered a new air drier this week from Truck Pro Truck parts. Called FT To see what air drier was put on my 96 8.3 new and I gave Truck Pro the information standing in my shop .. I can't get myself in position to look for a tag on the old air drier because of where it's mounted and my young mechanic wasn't here. Replacing it for PM purposes as it doesn't look like it's ever been changed. This post leaves me with having "compatible" questions before I even get the new drier. Truck pro ordered drier based on what parts dept at FT told me.Seems 3 line vs 4 line is the difference. Without a clear answer I suppose if my old drier is 3 line and I replace with a 3 line it should be compatible.... yes or not necessarily??
Dub,
The safest way to purchase a new or rebuilt dryer is to remove the old one and take it to a NAPA store. Lay it on the counter and say "I need the exact replacement for this thing". 9 out of 10 times they will have in stock, or can order, exactly what you need.
Since you have already ordered a dryer, you might as well wait until it shows up. Compare it to the old one that you or your mechanic removes from your coach, and see if they match up. If not, either exchange it for the correct one, or get a refund and go to NAPA.
That's what I aim to do Chuck..Would think it would be fairly straight forward on a 96 Cummins air system.
The SKF Turbo 2000 comes with a remote mounted purge tank. It is basically a ping tank. They have a Turbo 3000 model that ia self contained and that would have been fine, but the price difference is minimal and the extra work of finding a place for the ping tank isn't a big deal, but the larger capacity of the Turbo 2000 (also available in a dual HC version) seems like it might be worth having. Today I mounted the ping tank alongside the chassis battery next to the bottom of the radiator. I reused the Haldex Pure Air Plus mounting bracket by shorting the clamp band by cutting it in half and overlapping it and drilling a hole through the overlapped pieces. I then countersunk a flat head screw through the tank side of the bracket to pin the two halves of the band clamp in place, I attached a scrap piece of ⅛" 2" X2" about 20" long angle iron to the chassis battery supporting frame to make a ledge for the tank mount. Just to be safe, I will add a hanger of some kind to the radiator support bracket to secure the other side.
I also removed and inspected the unloader valve. I will make another post about that...
Some more pictures of the air dryer mount and its location opposite the Holset air brake compressor as will as the purge (ping) tank.
Don
I'm not clear about the purpose/function of the "ping" tank.
It's a local tank used to deliver brief bursts of air faster than what can be delivered by the supply line.
OK, but why does Don's air dryer require a ping tank. The air pressure used to purge the dryer is usually contained within the air dryer housing. Other air dryers work fine without a external pressure tank.
Perhaps because this dryer has a smaller, slimmer housing it does not contain sufficient volume of pressurized air to facilitate a effective purge?
The Turbo 3000 unit in which the purge air volume is included within the cartridge is listed as suitable for light to medium duty applications. The purge tank stores clean, dry air for regeneration of the desiccant bed. The self cotained Turbo 3000 would be adequate based on the Holset air compressor in our coach of around 12 CFM and normal use, but the greater purge volume of the separate tank provides extended compressor cycles which can only be a good thing. Since the price difference is minimal (and who's afraid of a little extra work ::) ), I decided with the higher capacity. Below is a screen shot from SKF showing the vocational matrix (why not call it an application guide?).
Don
A size and form factor comparison of the Haldex dryers VS the SKF, plus a few pictures of the D2 Unloader ASSY combo,,,
Assuming we can make it to Quartzsite this time, I can bring the OEM Pure Air Plus to give away at the raffle... ;D It should be a good science experiment and I suspect it is rebuildable.
Don
OK so after all of this, Is it fixed?
What's the rush? :D No, I am waiting for a rebuild kit for the unloader. Ridiculosly expensive for what is included. $102 shipped for this: 3559568K by HALDEX - Compressor Repair Kit (http://www.finditparts.com/products/363018/haldex-3559568k)
Aside from that, I will be replacing the protection valve, 2 check valves, adding a service air at the rear, and hopefully rebuilding the 6 packs...
P.S. I am posting the pictures and my conclusions etc., because I am learning more about the air system and want to share with someone down the line. Maybe it will help someone as pictures, part numbers, proceedures, etc. others have posted have been a big help to me for other projects, and I will be more likely to remember what I did.
Don
Because when you've spent $160,000 on a PhD . . .
" . . . a rebuild kit for the unloader. Ridiculously expensive for what is included. $102 shipped for this: 3559568K by HALDEX - Compressor Repair Kit."
Hydromat in Missouri builds a nice rotary transfer machine and we used to pay those prices for pretty much the same amount of stuff. It's what happens with limited production machinery.
Don, to Roger's question am I correct that in essence it is fixed after you took off the unloader valve body and cleaned the carbon etc off. You did mention that it worked but stuck again. The new dryer etc is just more refining of the system which you are good at and enjoy doing.
So, if anyone else has a similar problem with lack of air build up there is a real chance it can be fixed by taking that off and cleaning.
Johnh
John,
I have yet to reinstall the unloader ASSY as the gasket was trashed. Not easy to clean the gasket remnants off the compressor flange while the compressor is still on the coach. It would have been a whole lot easier if I had access to a pit! ::). The rebuild kit is supposed to arrive tomorrow. But since I had managed to get air to build twice with normal function, I am confident that reinstalling the unloader valve will restore normal function. However, you are correct, I am upgrading the system with the new SKF Turbo 2000 dryer as well as taking care of other air system maintenance while I have it up on the ramps. I had apparently two major issues with the system as the air dryer had failed as well. The OEM Pure Air Plus was rebuilt (supposedly!) in Canada, but always had issues in that the wet tank would always leak down rapidly to about 30 PSI after cut off was reached. That resulted in rapid cycling even with the engine idling and no use of the brakes, but allowed normal operation while driving the coach. It has bugged me ever since because I don't like anomalous behavior. The air dryer failure this time resulted in the wet tank not being able to hold air at all. I diagnosed this by adding air directly into the wet tank via the service air supply with my trusty harbor freight compressor. It wouldn't hold air until I bypassed the dryer. With the bypass in place, I was able put a 120 psi in with the external compressor. Not only that, after sitting all night the wet tank was still holding air at around 115 psi! So my conclusion is that my suspicion of the hack rebuild job of the OEM dryer in Canada being the cause for the rapid cycling is correct. I look forward to once again having a (relatively) air tight system again. Replacing the check valves, rebuilding the 6-packs, replacing the protection valve, is something I have been wanting to do for a long time. I will be installing the check valves on the brake tanks using stainless unions so that (as you well know!) the entire plumbing tree won't have to be disassembled to get at the check valves, regulators, etc.
Don
Don
Don, on the dryer leak down problem it sounds to me that it may be the same issue I had after FT rebuilt mine about 2 yrs after I bought coach, and my first trip to the mothership. The little check valve in the end of the main line at dryer was put in backwards so leaked back. Since my air tanks hold really good after fixing numerous little leaks a few years ago and doing the 6 packs. One holds 110 for a week and the other has a very small leak below brake pedal. Tough to get to tighten those line fittings. It still takes about 4 days to leak down to 30lbs.
JohnH