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air dryer problems


alex g
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I had problems with my old air dryer the vent on the bottom was not sealing so I replaced it with another used AD-4 dryer.When I installed the new used dryer my compressor would run about every minute or two.I bypassed the dryer to get by for now with it.I'm wondering if the problem is the dryer or I was told it could be the unloader valve in my compressor does anyone know how to test this before I replace anything unnecessary.Thanks

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the AD4 and AD9 are pretty similar, if the purge valve was leaking on the old one and putting the new one on has it running all the time I am guessing you mean the purge valve is popping off every minute or two. If so yes the unloaders in the head of the air compressor could be bad, its a simple $40 seal kit that takes about 20 minutes to do start to finish, also a constant purge signal can mean a leak in the unloader line from the dryer/tank to the governor. I dont know how your truck is set up but Im gonn guess the governor is on the side of the compressor and the dryer has the large hot air line from teh compressor, then the dry air line to tank and two 1/4" lines, one to tank and one to the governor. make sure your 1/4" lines are not leaking with some dish soap and water in a spray bottle, listen for leaks and watch for bubbles from one end of the 1/4" lines to the other, if there are no leaks there get the bendix unloader rebuild kit, it will have 2 springs , 2 back up seals, 2 o rings and a gasket, remove the batwing shaped plate on top of the compressor and remove the unloader valves, replace the seals on the valves, clean the sealing surface of the plate ans re install the valves and plate with the new springs, dont over torque the bolts that becomes a bad day.

"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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I think the unloader kit is a p/n 107515, I cant find it in my book here but that sounds right for a tu flo 750.

"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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to test the air dryer I use a air hose and blow gun take the 1/4 in line off the air governer that controls the air dryer purge valve and insert blow gun each time you apply air to hose it should purge then seal if this is good work on unloader as superdog outlined

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