2006 freighter m2 Air pressure problem

Hello everyone. This is my first post hopefully someone can lead me in right direction because I’m lost. Wish I found this forum long time ago lots of great info. I have a 2006 freighter m2. It’s a single axle 18yd garbage truck. I am having a air pressure problem. So I’ve never ran into a problem like this so I hope my description is clear. I first started having a air problem 2 months back. I would lose pressure when the maxi button was pushed in. I could hear the air leaking threw Maxie on dash and being a garbage truck we replace them more then normal because it’s all stop and go so I replaced it. Problem was still there so I next went to brake can. With the brake on and my foot on break no problems so I blocked the truck released breakes and I heard a descant air leak and found it coming out off the bottom of this valve bolted to frame which turned out to be be part of abs system so ordered valve which came with the whole valve system for abs and the brake value all in one all bolted together so it worked out. Installed it same problem. Now I’m like wtf. So I was like it’s gotta be break can but the break can wasn’t leaking air when I stepped on brake like every other break can has done in my 20 years of changeing them and the van was only month old but I changed it because what else could it be sure enough I had a defective can. I know because I benched it. So after changing I was running again but something still wasn’t right. In the next 2 weeks problem again. End of day I ended having 3 defective cans. Which I benched myself to be sure and was refunded by freighter because they tested also and said yup defective. Now bought 2 new different brand cans and still I have a problem. So now being frustrated I had my mechanic put a new compressor (needed one anyways) I replaced whole air dryer. Still not right. So I’ve replaced compressor,air dryer all the abs and break valves both air cans and any leak I can find and I’m still losing significant pressure. Mainly in one of 2air tanks. So this is where I’m confused. I build pressure in one tank hits 120 and I hear the air dryer piss but the other tank never gets over 100 and when I step on brake pressure goes down very fast especially in 2 tank but if I turn truck off pressure holds fine but with truck running in neutral I’ll keep losing pressure?? Only thing I can think is I have a hose somewhere rubbing that has a hole but why only when I’m running?? Is there a smoke system of some sort that u can run threw air system to find a leake??? Any help would be greatly appreciated thanku

 

Anyone??

 

I hate to be a nucence but if anyone can help me it be greatly appreciated

 

It’s a cat c7

 

Fan hub? Interesting because I noticed today my fan is always spinning. Normally the fan clutch comes on at 200 degrees brings motor down to 150 then releases. Today I never got over a 100 degrees fan ingagged all day.

 

That is exactly what’s going on!! Fan ingaged all day. Truck off no pressure loss. I actually noticed today for the first time the fan on only because it was cold and I couldn’t get over a 100 degrees all day and was like another problem great.