Air Pressure Drops When Ignition OFF

question how does the buzzer go off with the ignition off

 

BINGO.

Ignition off = dead truck. Otherwise buzzers would drain batteries by morning with no air in them.

 

If the truck has an air leak when shut down, it has an air leak when running. The compressor is keeping the system charged. This is over working the compressor and will lead to an early failure of the compressor.

It needs to be found and repaired. Air leaks can be very time consuming. Not one of the most popular things to work on.

Can you be cited for this. you could, depends on the officer.

 

i gotcha driver just messing with you.

 

Air leaks are a constant chase. You have a lazy mechanic. Here's what you need to do to find all the leaks.

Get a spray bottle and fill it with water and a splash of dishwashing soap and get about a three foot length of hose. Run the engine until you hear the cutout of the air pressure at about 125 psi and then shut off the engine.

If you can hear an air leak, but are having difficulty locating it, use the length of hose like a stethoscope. Otherwise use the spray bottle and start spraying all the connectors. Leaks will immediately bubble. It's almost always the connectors that will leak.

Once you have identified the leaking connectors take pictures and show them to your mechanic. He may be reluctant to do the work and I have a good idea why. EVERY shop I have been in use a tool to cut lengths of air hose. The problem is it leaves a sharp point on one side. When the end of the cut hose is inserted in the new connectors it will pierce the rubber O-ring and start leaking again. Insist that your mechanic does it the right way. He should shave off the sharp point and buff the end of the hose with fine sandpaper before inserting it in the connectors. Better yet get a plumbers cutter and stop using the cutter they have been using. Sure, it does take about a minute more to do it the right way for each connector, but they can stop the leaks.

Edit to add:. The spray bottle is also very useful for finding the leaks on a tire that isn't holding air. Valve stems are a common source of slow leaks.

 

60 PSI lost in 35 minutes is less than 2 PSI per minute average, which is still technically legal. But it might be losing air faster when fully charged, which could be a violation. If a mechanic can't find it, just keep an eye on it to make sure it doesn't get worse, and give a listen during your post-trip inspections to see if you can pin down the general area. Or the aforementioned spray bottle with soapy water can help too. I always have me some Simple Green.

 

Does it lose air that quickly when you shut down for the night as well, or mainly during loading/unloading?
I ask because the process of loading/unloading, with the weight changes, can cause you to lose air.

Also, losing 2 pounds per minute is still well within DOT regs for air loss when attached to a trailer.