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Air dryer purging every 10-20 secs on my superliner


scottwetzel
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Another thing that make the drier there purge too often is if the check valve in the drier is leaking draining the wet tank.On the mack like all trucks the air governor gets its air supply from the wet tank.So if the check valve on the drier is leaking back thru the open purge valve in the dreir the pressure drops on the wet tank and then the governor will engage the comp to charge up the wet tank again so it can lose pressure too soon and same old thing over and over. The 88 mack came out with a AD4 which had a plactic flpper check valve inside but the two wire AD9 which will go in the same brackets will have a out side screw in valve on the bottom which can be changed with out a tear down.

Had to re-read a few times to get it (maybe I got it!)...anyhow, I downloaded the manual for the AD4...the test for the check valve involves removing and capping the control line to the govenor and monitoring the wet tank pressure...was not real clear on what I was supposed to be observing with an external guage, BUT...without the control line hooked up, the compressor builds to 140 and stops, the if I fan off about 10 lbs, nothing happens just like it supposed to, fan off a little more and the compressor kicks in and builds up like it should. SO...the problem is definitely the dryer, will read more and try to figure it out...Thanks for all the comments...I am half way there!

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Had to re-read a few times to get it (maybe I got it!)...anyhow, I downloaded the manual for the AD4...the test for the check valve involves removing and capping the control line to the govenor and monitoring the wet tank pressure...was not real clear on what I was supposed to be observing with an external guage, BUT...without the control line hooked up, the compressor builds to 140 and stops, the if I fan off about 10 lbs, nothing happens just like it supposed to, fan off a little more and the compressor kicks in and builds up like it should. SO...the problem is definitely the dryer, will read more and try to figure it out...Thanks for all the comments...I am half way there!

Had another thought (my brain is getting me closer, albeit very slowly!)...the reason it seems to me like the compressor is not unloading is that I never see a drop on either gauge, WELL, if all my check valves are working, I would never see a drop in the WET TANK! VIOLA! I think I understand! I still dont know where the air is going to drain the wet tank, but I believe I have found the issue!

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Already have a nice air hookup to the wet tank...it is how I get it out of the shop quicker! Air it up and go!

Just got back from a nice long ride, I left the control line off of teh dryer and the air system performed like it should...I have never seen the air below 130 before now! It goes down to cut-in pressure and fill's her back up!

WIll either get a rebuild kit or replace with a reman AD-9...anyone got any experience with the swap? Or insight on how the AD-9 is different than the -4?

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AD-9 is a bulletproof dryer, the rebuild is straight forward and consist of some o-rings, a spring and the actual purge valve center section, comes apart and back together in about 20 minutes. the dessicant cartridge can be a pain to get broke loose, I use a big filter wrench or chain wrench but once broken loose it screws right off and back on. Itll be about $40 for the rebuild and $60 for the cartridge, never do just one do both at the same time once a year or every 100,000 miles.

"Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin

"If your gonna be STUPID, you gotta be TOUGH"

"You cant always get what you want, but if you try sometimes you get what you need"

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The AD9 will work in same bracket and connect same way as the AD4, however you will need to use a two wire connecter to the heater elemet were the AD4 use one wire.

Thanks for all the input...I'll get the best price for an AD-9, weigh it against rebuilding the AD-4...

Curious, I assume the second wire is ground? I can just run a short jumper to the frame?

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The AD-IP is a good dryer, but its just as cheap to buy a new one as to rebuild it with a cartridge and purge valve kit. As for the heater like above if its a part time use antique truck and you keep the water out of the system and dont use it much below freezing its no big deal, also the heater is really only needed for about 20-30 minutes after startup. Once the engine and compressor are at operating temp the air going thru the dryer is over 100degrees therefore hot enough to not freeze up. I actually dont have one on the superliner, I have an AD9 in the garage for it but I use it so little it just hasnt bothered me yet, I still drain my air tanks every time I drive it and do with trucks with air dryers also so its not a big deal for me.

"Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin

"If your gonna be STUPID, you gotta be TOUGH"

"You cant always get what you want, but if you try sometimes you get what you need"

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  • 6 years later...
On 10/23/2014 at 3:54 PM, rsb502 said:

Always, always, check the unloader side of the system first for this issue, if its not an unloader line leak its the unloader seals 95% of the time. Changing governors wont fix a recurring dryer purge, changing compressors only fixes the issue if the unloader seals are bad and its a whole lot cheaper and easier to replace the seals than the whole compressor. I think Ive fixed this same issue a hundred times maybe more, its a very common problem, I used to keep a squirt bottle with soapy water and an unloader rebuild kit on my toolbox when I worked at Howard Baer it was so common. Glad you got it fixed before you spent big money on a compressor.

I have a 2006 frightliner and when I reach my max pressure which is set at 140 it doesnt purge right it purges super super slow and when im driving it builds air to high and cant purge air fast enough so my pressure gets super high and I have to hold air hose inside truck on or keep hitting breaks plz help

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try a new D-2 governor. is yours bolted to the air dryer on the front of the torpedo tank with the air dryer?  Make sure there isnt any water in the tanks,also, Jojo

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