Ken,
I have had an ongoing issue with the air dryer popping off about every 5 to 7 minutes while at idle... Is that what you are experiencing? What suggestions did James have for you? While over the pit at John Haygarth's, we found and fixed several leaks but they had no effect on the cycling air dryer pop off. Obviously a leak of some sort, I am just hoping that it isn't internal to the compressor. The air dryer was rebuilt prior to my stay at the pit (unsure of the quality of the rebuild, but I couldn't get the parts at the time to do it myself).
Don
Don,
Is the air compressor cycling along with the dryer? Do you have a pressure gauge on your wet tank? If yes, does the wet tank pressure go up and down in concert with the compressor operation?
Don,
There are a lot of Internet posts on this topic of rapid cycling. From what I can see it can be several different causes, need a dryer rebuild to a leak in the air control line from the governor.
I had my AD-4 dryer in for routine service and was told it is obsolete and parts hard to find. I upgraded to the AD-9. Cost was $800, new dryer $280, labor $520.
The wet tank pressure does go down fairly rapidly when the engine is turned off, but I haven't stood at the back of the coach while the engine is idling to watch the gauge (I tapped of off one of the extra ports on the governor and mounted a gauge that is visible from the back with the hatch closed), but that is an obvious next move now that you mention it! However, I feel pretty sure that the wet tank leak down is what causes the compressor to cycle. John and I serviced all of the check valves and used a soap solution to check for leaks, but the leak must be an internal one. I purchased new check valves just to be sure, but haven't put them in yet. I also bought a brand new (old stock) military surplus air dryer and an isolation valve to adapt it to our coach, but haven't done that yet. I figure I will tackle all of that along with the six pack plunger rebuilds at the same time. Well, I will do it in increments so I can check it the function at each step!
Don
Peter, my searches on the topic yielded much the same results... as far as I can tell, the air control line is not leaking. I also put new JIC fittings on that connection when I put the rebuilt air dryer back in. The Holset air compressor used in our coach (I think they went to a different compressor in 2000), requires what is called an isolation valve and that is kind of a wild card as far as diagnosing this issue goes. I scored a couple of new old stock isolation valves on eBay, and I put in a new one and it didn't make any difference.
Don
Don, have you checked your D2 govenor? I had the same cycling that you describe awhile back and found the leak on the gov.
Good luck.
Don,
When you get back to this project look at the line on the isolation valve that should be tagged 60. It is the 1/4" black nylon line that comes off the isolation valve and disappears up the frame rail. This line terminates on the wet tank. Drain the air from the wet tank and remove this line from the fitting on the wet tank end. Now remove the fitting itself. This fitting should be a check valve/fitting combo. Make sure the spring isn't broke or full of rust as this will cause the isolation valve to stay open.
Pamela & Mike
@Don,
Already a lot of good suggestions here. James says there is a piston(?) involved in the pop off process at the dryer that can fail and cause fast pop offs. I asked if that part was replaced during a rebuild. He said no (don't know if this only applies to the Haldex). I had previously talked to Alton who thought it might be an air leak in the line to the dryer or wet tank. He said he pulls the line from the dryer, puts air pressure on the line with a compressor, and uses a gauge to check leak down. He must have a custom adaptor to do this. Would not be hard to make one. Mentioned this to James since I had talked to Alton first and James agreed that could be it. James also said I wouldn't be doing any damage running with the cycling. I will continue to keep a close eye on the air gauge while driving.
I have bigger fish to fry right now so have put this off for now. I'm leaning towards replacing my dryer with an AD-9. Found one for $250 (new) on the net but doesn't look like I bookmarked it. :( Will post link if I find it. Will test for leaks in the lines when I have the dryer out. Has to be a pretty good size leak to be popping off as fast as it does.
EDIT: I did change out my D2. It didn't help.
see ya
ken
I would bet on the check valve at the air dryer. The compress will come on, until it get the signal to cut off. Once it is cut off the air bleeds back thru the check valve, lowers pressure and it all starts again. When I had this problem the pressure gauge at the dash stayed close to the full mark all the time.
Found the link to the AD-9. Duh! Search browser history! :)
Price is a little more than I remember. $295 for AD-9. $19 for wiring harness. Yikes $43 shipping to Colorado.
Bendix 065225 12-Volt AD-9 Air Dryer with Mounting Bracket Kit (No Wire... (http://www.anythingtruck.com/product/060-065225.html)
PTP 109869 Heater Wire Harness Kit for Bendix AD-9, AD-IP, and AD-IS Air... (http://www.anythingtruck.com/product/060-109869N.html)
see ya
ken
Don,
Please clarify, your coach should have came equipped with a Pure Air Plus, is this what you have now or has it been changed to an AD-9? Even though they do the same thing (drying air) they are made and operate differently.
Pamela & Mike
I should have put that in the first post P&M! It is the original (Pure Air Plus, I believe) . The new old stock one I got on eBay is also a Haldex, but it is called a "PURest". The connections appear to be identical with the exception of the dryer. This one has a 24V or maybe a 36V dryer. I will have to swap it out or get a new 12V element. The mounting is different, but I will drill the new hole pattern on the original mount. I have a new isolation valve, so while it isn't exactly the same, I believe that I can adapt it. I also believe that this one has more capacity from what I read awhile back, but I am not positive. Physically, it is actually a little larger... but nothing a shoehorn won't cure ::) .
Don
It could be, but if you're referring to the one in the dryer itself, that was replaced. I even checked the orientation of it to make sure they didn't put in backwards.
Don
Yes, making a test fitting to add to the tool kit sounds like a good idea to me... I also change the D2 (twice!), but that wasn't the problem.
Don
Thanks P&M,
Are you referring to the main check valve on the wet tank (I thought there was just one)? John and I changed that diaphragm, but I do have a new valve to put in. Actually, I have three and plan to change out all of them. Is there another one that is just on the isolator line? If so, that sounds like an excellent candidate to be the trouble maker!
Don
Don,
1. No this one is totally different than the one that is the KN-23000 main check valve.
2. Yes, It should be built into the 1/4" brass fitting (all that I have seen are 90* fittings) where the #60 air line ties into the wet tank.This fitting is in a separate boss that is welded into the tank. Sorry I can't get a pic. of the fitting and location for a while.
Pamela & Mike
Don,
I have been looking around through my paperwork for a part number for that fitting but no success. I do remember I took an old one to the Parker Hannifin fitting store and they came up with one.
Pamela & Mike