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Air Dryer/compressor Questions

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I installed a new air dryer on my 98 CH. Right after it spits it sounds like air is leaking from the compressor but only for a few seconds. Why does it do this??? There doesnt seem to be any leaks around the compressor. Also the compressor charges my system up to 130PSI. Is there a way to dial it down???? Is there any special way to install the air dryer besides mounting it and connecting the 3 air lines and plug.? It was pretty simple...but almost too simple.

Thanks for your help.

Rob w.

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Rob,

The three lines and plug are all thats needed. As for the air leaking sound, the governor sends out positive pressure to hold the unloader valve in the compressor open. This stops the charge cycle and that same air signal also triggers the purge cycle of the air dryer.

The governor does have an exhaust port, that might be the leaking sound but thats normal. 130 PSI sounds normal as the pressure relief valves in the brake system are set at 150 PSI. Turning that pressure down is possible by adjusting the governor cut out pressure via a screw on one end. But some governors are not adjustable like the D2-A from Bendix.

Here are the instructions for the D2 from the Bendix website:

To raise the pressure settings, turn the adjusting screw

counter-clockwise. To lower the pressure settings,

turn the adjusting screw clockwise. Note: Be careful

not to overadjust. Each 1/4 turn of the adjusting screw

raises or lowers the pressure setting approximately 4

psi.

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I'd leave it at 130.

That extra 10 lbs. pressure isn't going to hurt anything, and it will give you an extra reserve of air.

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Some of the newer air driers like the Bendix AD-SP have a longer purge that will sound like a air leak from the bottom valve, but only for 10 seconds or so.

Chuck

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Unless the destroking process on the air compressor takes longer than the purge, It will continue to pump air untill the destroking valve hold the valves open on the air compressor. Just had a 3176 cat in a t600 KW (part of Maxvilles fleet) that would continue to pump all day long. The culprit, a collapsed line from a governor to the compressor, but if your mack is like mine, the gov is bolted to the comp. Also, The o rings on the destroking valves could be old and cracked, I just ordered a "destroking kit" for the bendix tf 550 air compressor on that cat(the same as on my truck) that consists of a gasket and push rods with new o rings for a whole 15 dollars. Those valves are just under the cover on the head of the comp(right on top). If you need i can get a part #. Let me know.

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OK gang i still need your help. I installed a new unloader kit in my 98 CH. It didn't really make much difference but my air dryer is doing silly shit. It is a new dryer from the Mack dealer....When i start the truck with 0psi its fine until the dryer spits at about 125 (sometimes 130) then it ticks like a bomb for 5 seconds then it hiss's air until the red needle is down to 100. Air builds back up (dryer still hissing air) until it hits 125/130 again. Then it starts over. It seems to hiss air all the time and the compresor is just doing it's normal thing. Is the new dryer bad?? The parts guy at Mack said they are really never bad out of the box.

thanks for the help

Rob W.

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OK gang i still need your help. I installed a new unloader kit in my 98 CH. It didn't really make much difference but my air dryer is doing silly shit. It is a new dryer from the Mack dealer....When i start the truck with 0psi its fine until the dryer spits at about 125 (sometimes 130) then it ticks like a bomb for 5 seconds then it hiss's air until the red needle is down to 100. Air builds back up (dryer still hissing air) until it hits 125/130 again. Then it starts over. It seems to hiss air all the time and the compresor is just doing it's normal thing. Is the new dryer bad?? The parts guy at Mack said they are really never bad out of the box.

thanks for the help

Rob W.

Where does the air leak fromand what kind of drier is it? glenn

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Unless the destroking process on the air compressor takes longer than the purge, It will continue to pump air untill the destroking valve hold the valves open on the air compressor. Just had a 3176 cat in a t600 KW (part of Maxvilles fleet) that would continue to pump all day long. The culprit, a collapsed line from a governor to the compressor, but if your mack is like mine, the gov is bolted to the comp. Also, The o rings on the destroking valves could be old and cracked, I just ordered a "destroking kit" for the bendix tf 550 air compressor on that cat(the same as on my truck) that consists of a gasket and push rods with new o rings for a whole 15 dollars. Those valves are just under the cover on the head of the comp(right on top). If you need i can get a part #. Let me know.

You may have bad unloder orings in the compressor head depending on your compressor they can be easy or hard to change!

If you have a 700 bendix its easy if you have a 500 bendix its dificult!

take the small line off the air drier while the compressor is pumping between 90 and 130 if there is air coming out the line the problem is in the unloader !

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Where does the air leak fromand what kind of drier is it? glenn

The air is coming from the valve or hole at the bottom of the dryer. I dont recall what model Bendix it is.

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There is one thing i forgot to mention...when i put the new unloader kit in I had a problem with the gasket leaking and took the cover off again. I did notice the piston on the left side popped up with the new spring and the right one (the one to the front of the truck) didn't pop up and almost seemed stuck in the hole. I did grease the new ones up with the grease in the kit before i put them in.. Was it supposed to pop up when i took the cover off????

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There is one thing i forgot to mention...when i put the new unloader kit in I had a problem with the gasket leaking and took the cover off again. I did notice the piston on the left side popped up with the new spring and the right one (the one to the front of the truck) didn't pop up and almost seemed stuck in the hole. I did grease the new ones up with the grease in the kit before i put them in.. Was it supposed to pop up when i took the cover off????

If it drains the air tank down till the governor kicks back in and it is a ad4 or a ad9 bendix you have a check valve in the drier draining the 1st tank back in to the drier and out of the purge valve. The ad 4 has a plastic flapper for a check valve inside and you have to tear down to replace and the ad9 will have a screw in check valve on the bottom on the inlet port of the dier and can be changed from the bottom. glenn

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The part # on the box is 745 800887 it says AP-SA Bendix air dryer it doesnt have a number after AP. I'll look on the air dryer itself on Monday. The old one doesnt say either. The new one does have a plastic flapper on the bottom.

So what you guys are telling me the air dryer is probably the problem and not the compressor or unloader?? It's still under warranty. Also the Mack dealership said I can bring it in and they'll test it.

thanks again

Rob W.

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My bad ...it's AD-SP

I sorry but i cant help you on the ad sp i know what it is but have never wored on it but if the dier is draining the wet tank it sounds like the deir is defective. glenn

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