I think my air compressor is cycling to much.

[spankybear]

When I drive down the road I hear the air dyer purging all of the time. About every 2 mins or so. I am in no way an expert on air systems on these trucks but let me tell you what I think I know. The air governor unloads the compressor when it get to the set pressure. That is PCHISS I hear from the air dryer. Then when the air drops below the low set point the governor kick the compressor back on line. This fills the wet tank . The outlet of the compressor goes through the air dryer. I think I have that right.

So I am not clear that when the compressor is unloaded is the supply line from the compressor open to atmosphere? I believe there is a check valve after the air dryer and before the wet tank?

The truck holds air over night but goes down a tad to like 80 PSI or so. I don't think this would be a large enough leak to keep the compressor cycling like it does. So I am thinking that a leak maybe before the service tanks.

With all of that said is the a common issue with leaks on the air system.

Can you troubleshoot with charging the from remembrance glad hand?

 

[simp5782]

Compressor is seeing the wet tank pressure for its cut In and cut out pressure your other tanks are not leaking but your wet tank is leaking down causing the pressure to continue to cycle on. Your check valves on the other tanks are doing their job by not allowing back flow to the wet tank


This happens on trucks where there trailer systems feed off the wet tanks even a slight trailer leak the Compressor runs alot but the gauges never move

 

[Ronmar]

You are correct, when the compressor unloads the line from compressor and dryer are open to atmosphere, because the governor has opened the purge valve at the bottom of the dryer.

what is the difference between parked and driving? You are applying park air to release the park brakes. Does it purge every 2 minutes while just setting with park air off/park/spring brakes applied?

You could be loosing air thru the park 2way valve under the drivers floor. The quick check for this is to chock the wheels, start the engine, release the park brake/apply park air and see if any air comes out the front emergency glad-hand vent...

If not, shut off the truck, leave the chocks in place and connect an air compressor to the front emer glad-hand. This will pressurize the air system and apply park air, then start looking for leaks

 

[spankybear]

It unloads the same when parked or driving. I also hear a noise when the compressor is building pressure but don't know if it normal or not. The tone changes when I turn the steering wheel... I have uber sensitive hearing and hear things most people can't. I know the power steering pump is on the back of the compressor. First thing is finding the leak and I believe it maybe between the air dryer check valve and the compressor.

 

[simp5782]

Pull the line at the compressor and rig your shop air into it to fill the truck there so you can better hear with the truck off. You may have super good hearing but you aren't going to hear an air leak with that rackety cat running unless it's a big leak


Also tap a gauge into the ctis port on the wet tank to see what it is doing maybe a T fitting so your ctis can still operate and see if it's on that side

 

[Ronmar]

Yep, gotta hook up a compressor and find the leaks. Even the most sensitive hearing can miss things when the cat is purring

 

[tennmogger]

Big clue: wet tank drops to about 80 psi. The Pressure Protection Valve turns off, closes, at about that pressure. That means the leak is either the CTIS circuit or the cab suspension air system, both of which run off the wet tank. Try turning off the cab suspension with the locking button on the hydraulic control panel. Fixed? No? Then unplug Ctis controller to disable ctis. Fixed?

 

[spankybear]

Big clue: wet tank drops to about 80 psi. The Pressure Protection Valve turns off, closes, at about that pressure. That means the leak is either the CTIS circuit or the cab suspension air system, both of which run off the wet tank. Try turning off the cab suspension with the locking button on the hydraulic control panel. Fixed? No? Then unplug Ctis controller to disable ctis. Fixed?

You know looking at the air diagram I see the fan clutch is also on the wet circuit... Another clue is when I start the fan is on... but the two service tanks has some air in them. It maybe the cab ride height valve leaking. Are these rebuild-able?

 

[spankybear]

I have not been able to fine a leak but have noticed that the compressor doesn't cycle as much when its warmer out. So I thought Iwould service my air dryer. Well it seems that the army has busted the plastic desiccant canister and the aluminum cylinder edge looks to have been attacked by a angry beaver. So do I replace the damaged parts (if I can find them) or just replace the entire dryer? I h ave a lead on one of them A1 styles

 

[Coffey1]

Mine was doing it
And it was the drain valve on wet tank cracked open

 

[Mullaney]

You know looking at the air diagram I see the fan clutch is also on the wet circuit... Another clue is when I start the fan is on... but the two service tanks has some air in them. It maybe the cab ride height valve leaking. Are these rebuild-able?

.
When I discovered the air ride knob on the passenger side by the tool box I was excited. I hadn't really even known it was there or that it was an option. Standing outside, I didn't see the cab move so I wasn't impressed when I turned on the air ride. Then I went for a spin down the road and noticed that it rode a lot better. Still - I hadn't really noticed what was going on.

Next day, I climbed in and cranked the truck. Air was at about 50# in both tanks if I remember. The buzzer was going off for sure. As it built air, the buzzer turned off and I started feeling the back of the cab lifting up. I wasn't prepared for that! I was giving serious consideration to jumping out of the truck... (Yeah, I felt like a complete fool at the time!)

Now - With a little more experience that tip up from the back of the cab happening at 90psi - I know that it is normal. It also confirms things in the air system are operating properly too.

I would imagine with house air applied to your truck you should be able to hear a leak on those air bags.

CHOCK YOUR WHEELS, then get a spare glad hand. Attach that new glad hand to a shop air line with a quick disconnect - just like any other air tool.
Disconnect, then put the glad hand on your truck glad hand (the red one) then plug in your house (shop) air. That will pressurize the system with the motor off. If you have a leak that will make it easier to find. A lot easier than with the truck running.

 

[ckouba]

As an aside, what is the frequency/duration at which the compressor should cycle/dryer should purge?

 

[Ronmar]

As an aside, what is the frequency/duration at which the compressor should cycle/dryer should purge?

Dryer purge rate is a factor of air consumption. The dryer purges every time the compressor reaches cutoff pressure and unloads. If you started your truck and let it run for an hour without touching anything, in a non-leaking truck, I would expect it to purge once shortly after startup when the tanks are topped off and not purge again for the duration of the run.

I would expect it to purge more frequently when CTIS is filling tires, perhaps every 20-30 seconds.

If you are wheeling or using a lot of brake pedal, it will cycle based on that usage, after every 5 or so full pedal uses In a 4x and maybe less in a 6x...

if the truck is purging regularly and you are not doing anything, you got leaks...

 

[ckouba]

Thx Ronmar. I figured it was usage dependent but your first and last paragraphs were the most helpful to me.