Air Compressor for an Cummins ISX question

check for air leak at fan hub.

 

I did as you said, built pressure as high as I can, turned off the truck and turned the key to the on position, heard no air escaping but went back in to turn the key off the (R) air pressure was back down to LAW the (F) was just a little lower than where it was when I shut it down.

 

Ok, at this point this is what I would do:
Remove drain from secondary (R) air tank. Install a male quick coupler in the hole and connect shop air hose regulated at 125 psi. This will give you all the time you need to locate the leak in the secondary.

 

okay thanks, do you think it couldnt be the air compressor going bad?

 

I highly doubt it.

 

Why is it effecting both the (F) and the (R) tanks? and also why is it stopping building pressure when the fan cuts off? Sorry to be asking so many questions I dont know much about this area and would like to learn as much as possible.

 

The F tank feeds the R tank with a one way check valve between the tanks,
The only way the fan would have an affect is if the fan hub leaks air when released and you already checked it for leakage. The engine fan is air release isn't it?

 

What is the max air pres. the truck will build?

 

Most systems are designed to cut out the compressor at 125 psi. This considered normal for most trucks. Some other applications let this go 135. Compressors, air driers and some air tanks come with safety blow off valves are mostly set 150 psi.

 

I'm sorry heavyd...I was wondering if the poster's problem was that the truck would not build air pres. or was real slow to build air pres. The fleet that I maintain has had these problems and it was a simple fix. If you remove the head off the compressor in most cases you will find that it's full of carbon from the Egr deposits. ### mins recommends that you clean it but I have found that this is only a temp repair. I use the head replacement kit and this takes care of the problem.