air system. need help!!!!

When you say air sep., do you mean the air dryer? If not , mine started this jazz and then quit pumping altogether and it was the air dryer assembly. Somewhere in the cost range of $300, pretty simple to change out, had to do mine on the road but had a basic tool kit made it work.
The new dryer if it is a Wabco should come with a new cartridge, they are a spin on like an oil filter. Before you do that , check the steel braided line from the compressor to the tank and make sure that it is not ruptured and leaking. Hope this helps...
J-J

 

Check the non return on the first air tank. Sometimes it doesnt seat well and it causes the air to shunt.