Air Dryer Purging Air Every 15 Sec

[GunRunner]

I recently purchased a 2014 Cascadia and had to have some driveline issues addressed and took it to a shop. While in the shop, they were doing a DOT inspection and said that the air dryer is leaking. They replaced the air dryer with a new one and when I picked the truck up, it is purging air about every 15 sec. They thought it was the governor and put a new governor on it and still does it. They then said they found the braided hose was leaking and had a new hose made, still doing it. Next, they warrantied out the air dryer and it is still doing it. They are stumped and so am I. None of these symptoms were present prior to the shop replacing the air dryer. With that said, could it be the unloader valve in the air compressor? That is the only thing that has not been touched. I have researched and searched on here and I am at a loss as to what it could be. Anyone else ever experience this?

[hookliftpete]

Compressor running constantly?

[GunRunner]

That's a good question but I'm not 100% sure. I think it is since it is purging every 10-15 seconds but don't know. I'm not super knowledgable how the system works and I'm learning

[hookliftpete]

Shouldnt be hard to tell if compressor is running constantly, should be able to hear it. Maybe double check the signal line from governor to compressor and unloader, also check for leaks that only occur while key is in on position, some things like the fan clutch only have air applied with key on. This is a cummins I assume?

[Rawze]

could also maybe be that someone got the plumbing wrong going back to the compressor unloader valve when installing the new one the first time?.

[JMBT]

Also check for leaks only present when the tractor brakes are released. It happened on my truck a few months back, air dryer purging every 30sec or so, but when I would get under it to look for leaks, the breaks were always set.. one day I set the trailer breaks and left the tractor supplied to check and found it immediately..

[GunRunner]

Thanks for the suggestions, the truck is still in the shop and if they can't figure it out by end of day Monday, I'll get the truck back home and start figuring it out myself.

[Bengy88]

Unless it’s some weird shi#t like JMBT had goin on If a shop can’t figure that out in an hour or less you need a new shop buddy. And that’s giving them a little time to play with. Most of the time it’s as Rawze said the governor is plumbed wrong….. or an air line is broken. Depending on how your governor mounts there is usually 2 air lines. For example a D2 governor will have 3 sets of ports, 3 will be labeled res, 3 will be unl, and one port is exhaust…. Never block the exhaust port. The “unl” port will go to the air compressor head and to the air dryer signal, the “res” goes to a main air supply. It’s literally that simple…. If the governor is plumbed correctly and the “unl” line to the compressor doesn’t have a leak but it’s still purging every 15 seconds then your unloader valves are most likely stuck in your compressor and when the governor sends the signals the compressor isn’t unloading so the air dryer is purging every time signal is sent.

[JMBT]

Mine was this valve. Rides directly above the front drive on my truck. Divides the air supply and sends to each of the brake cans to release parking brakes.. brakes set no leak, brakes released leak..