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air builds high pressure, purges every 15 seconds

Before - Air system builds to 125 psi in primary tank and 120 in secondary tank. Air Dryer purges approximately every 30 to 40 minutes.

After - Air system builds to 125 psi in primary tank and 120 in secondary tank. Air dryer purges approximately every 15 seconds.

Replaced air governor, air dryer heater and signal hose from the governor to the air dryer ( 1/4 inch hose on air dryer ). The system, then, would build to nearly 150 psi in primary tank and builds to 140 in secondary tank. The air dryer purges every 15 seconds.

Removed the air compressor head, cleaned the buildup off the head, also removed, cleaned and replaced the two unloader valves on the top of the air compressor head.

No change.

2001 Freightliner Columbia, 12.7 Detroit 470 HP.

I think the filter in the air dryer is plugged, that would cause the air to purge more often, but that does not explain the high pressure. I've put the old air governor back on and the pressure still builds high.

If I bypass the air dryer completely, do I need to put a 1/4 inch T fitting in the line from the primary air tank to the air governor and splice the signal wire into that, or just remove the fitting from the air governor to the air dryer and cap it off?

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I would strongly advice you to fix the problem. By-passing it will create bigger problems for you in the future. I found when air dryer starts giving you problems, get a new one rebuilding it never worked very long for me.

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I'm actually wanting to bypass the air dryer completely. Older trucks didn't have air dryers and I drain my tanks daily so there is actually no need for one for me. I just need to know what to do with the lines. I've searched the internet and am getting conflicting answers. Some say to cap the line, if that's the case, I can remove the fitting from the air governor; some say to put a T fitting in the line and connect it to the signal air line from the tank to the air dryer.

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I am just doing some figuring here, but do you have an alcohol resovoir for your air system? I would think all of the older trucks that did not have air dryers had an alcohol system to remove moisture. I would also think that the 1/4 lines need to be hooked to the primary tank, because, otherwise, how is the air governor going to monitor the pressure and regulate the compressor? It seems to stand to reason that if signal line is unnecessary if there is no dryer, it would be unnecessary with a dryer. I would keep the dryer and resovle the problem. You can maybe have an immediate fix by resetting the governor. Do this by inscrewing the black plastic cover, loosen the 7/16" locking nut on the screw, and then turn the screw clockwise to have the compressor shut off at a lower pressure. You are probably going to have to turn the screw several different times before you get the desired pressure cutoff setting.

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? Is the commpresor turning on and off with valve purging? Could there be leak in the system causing it to cycle so quickly?

Also, you began your question with "before" and "after". Did somthing occur inbetween?

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check valve in air dryer no good

you can plug signal line and hook 2 big lines together

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It's your unloaded Valves in your compressor had this happen many times

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If the dryer is a Bendix there is usually a purge valve at the bottom of the unit that needs to be replaced. The difference in the air pressure can be corrected by adjusting the air governor. If you choose to just by pass the dryer it can be done so with out any additional problems as long as you drain your tanks on a daily basis....''italic text''

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It was a lot of years before I owned a truck with an air drier, from the factory and then it was optional and NO, they did not come with alcohol systems, either. Your purge valve is bad, that is all. Disconnect the two big lines, from the drier and connect them together. Don't worry about the little line, just leave it hooked up to the air drier. Done this many times, over the years and never a problem.

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2002 volvo 770 looks like two purge lines in air system coming out of firewall in front of driver...top line continues to blow air. ....we plugged it off and trailer brakes wouldn't release...unplugged it and brakes released can't figure out why it continues to blow air...

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i'm sure you got it fixed already but you need to change the trailer brake application handle valve.

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