Low air alarm

yes, that is why i have been crawling all over this truck.

 

i have a buzzer going off intermittently and i think it is the low air warning buzzer, but no lights display on the dash. i replaced the low air pressure switch, but now this is happening.

i can bleed down the air (65psi) and the buzzer/light goes off when it should, build air back up and buzzer/light goes off. i then bleed off air, like when doing the governor cut in test, and the buzzer will sometimes go off, no light on the dash. i have even had the buzzer going off when pressure was built all the way up (120psi) again this does not happen all the time.

any ideas?

 

update: i have replaced the dash module and low air pressure switch, and the foot pedal air valve (was leaking), but problem still exists...

what the buzzer is doing know...when the air pressure hits about 65 psi, the buzzer turns off and air pressure continues to build to about 120 psi as it should. i can then make a couple of stops (actually driving truck) and the buzzer sounds (guesstimating 90-100 psi - kinda hard to know for sure because of the air gauges freightliner uses)

truck is a 93 FLD 120 with an N14, thanks for any help in advance

 

Are you sure you replaced the correct air switch, there will be others for brake lights and cruise kickout, parkbrake warning light...

 

heavyd... i know i replaced the low air warning switch, but not any of the others. could these other switches cause the buzzer to activate, yet the light on the dash not turn on?

speaking of the low air warning switch, what is the advantage of the normally closed verses the normally open?

 

Normally open or closed is just how the switch is in the running condition. Some switches will open the circuit when air applied and other will close the circuit instead. It is very important to install the correct one or that particular system will work opposite. Whether or not it needs a NO or NC just depends on how the circuit was designed.
Your problem is interesting. Since all the air stuff has been replaced maybe we should changed direction. I know the buzzer will turn on with low oil pressure too. The sensor for that is just another mechanical pressure switch like that of the air pressure switch. See if you can find it in the engine block somewhere, it may be getting weak. I am guessing maybe when you hit the brake the engine is also dropping to idle where the oil pressure would be at it's lowest. Just enough to intermittently trigger the warning. There still should be some kind of warning light too though. Hope this helps!

 

Both are your reserve air, one for your primary system, one for your secondary system.

 

Well if you wanna be that specific, you should have said "one for your primary air tank, one for your secondary air tank" as both supply the same "system" on the truck n' trailer. so far as I see it, I don't see any secondary breaking system in the brake drums when I'm nosing around in there.

Hahaahhaha...Oh I'm just being cheeky but hey, the little bit I know about trucks, I gotta chime in with something even if it's mostly irrelevant. Sorry Magna.

 

Lol, actually, the primary system activates the drive axles, and the secondary activates the steer.... The trailer is blended air.

 

been awhile since i have visited this thread, but i still have this issue. weird thing, when the buzzer sounds (as described earlier in this thread) I can flip on the headlights and the buzzer will go away (although not always) and I just recently figured out if I turn on the fan switch to the ac/heater, this will also cause the buzzer to turn off. I just keep repeating this cycle.

I also noticed when this issue happens, it depends on my speed/rpm. If I am driving through town traffic and this issue happens, once the rpms get above 1500-1600, the buzzer will turn off, lower buzzer turns on.

this is a very intermittent issue and so far i have not been able to track down the cause.