N14 wont hold 120 psi

CK. the line running from air dryer to air comp. find a place where its easy to hear the leaks you have to find, the air dryer you just put on was it rebuilt or new, stand by air dryer an listen after it spits for a leak at ex. port ?

 

Time to bust out the spray bottle with a soapy water mix and start spraying every inch of air line. The soap will make bubbles when ya find the leak.

 

If you have a wet tank with drain valves, leave them open overnight with engine off after the first initial spraying of a oily fluid that builds up in there too much.

If this is the case, prepare for a situation in which your air brake diagphrams in the spring side chamber and your air side is being eaten through eventually setting you up for a horrible game of drain my air the moment you slow from 70 to 25 or whatever it is you need to be at for a exit ramp. Both of your air Primary and secondary will drain at a rate towards Zero pretty rapidly if not faster than your speedometer is falling from 70 to 25 or whatever it is before your spring brakes are going to apply.

This happened to me because I never drained my wet tank which eventually caused several of the rubber diagphrams to be eaten through.

Most all trucks today have a air dryer that should spit and hiss every so often keeping you dry. That will be the next problem I look at.

 

I would keep it simple. You have an air leak you can't find. I would build up your air to 120. Shut the truck off and then turn the key on but don't start it. This engages the fan solenoid. Your fan clutch may be leaking but you can't hear it with the engine running. You should hear air leaking from the fan clutch if so.

 

How fast does it build air pressure from 85 psi to 110 psi? Could be that it does not supply enough air due to a restricted air discharge line from compressor to the air dryer

 

There should be nothing restricting the discharge line from compressor to dryer. But for sake of plain thinking maybe it is a good idea to check and be sure. Maybe a seal failed and got into it with pieces. I had a brake caliper on my dodge years ago suddenly ingest a failed seal and put pressure on the rotor and requiring another 200 rpm to maintain speed on the highway.

That is one idea.

85 to 110 or whatever should not be a problem. 110 is not bad, without being a parrot qouting chapter and verse of CDL manuals for air brakes, I need the system to be at least 90. Anything above 90 psi that it holds is a good thing. There should be a primary and a secondary in there to consider as well.

 

How fast it builds air from 85 to 110 psi gives you an idea of how much air volume gets from the compressor to the air dryer. To me it seems to build air slowly and doesn't maintain adequate air pressure while driving.. Which points to either compressor problem or restricted air discharge line. Line and hose from compressor to dryer. Doesn't cost an arm and a leg to check or replace. After rereading original post if aired up to 120 psi, how fast does the air pressure drop with the engine off and the parking brake set? If it doesn't drop fast try the same with the wheels chocked and the park brake released. See if that makes a difference

 

I had a big leak from compressor to dryer one time. not long ago. just replaced with steel braid line. was copper with 2 or 3 couplings in it. I could not hear it leak while truck was running. but after I turned truck off it would leak for just several seconds than stop. another leak I get at least once a year is in one of the lines going to the trailer, either the red or blue. some time the hole is too big for soap, yep the hole blew so much air pressure, it would blow the soap away from the leak.

 

also left key in on position & soaped fan clutch. was a whole lot of bubbles after about 15 min. but never dropped in pressure like yours is.