Freightliner Columbia air build issue.

If the compressor is working there has to be air blowing out somewhere.

Just to be clear, that means you replaced the purge valve in the air dryer, right? Have you checked to make sure there is voltage going to the purge valve heater?

 

I would start with the main line feeding your air dryer, i’ve seen the last few feet of the stratoflex (fiber cover) leak, not audibly, but with soapy water will look like it they forgot the rubber liner in that section.

If that’s good your unloader valve mounted in the top of the compressor is probably gummed up. 9 times out of 10 you can remove it. Wash it down, and (unless there’s a torn o-ring) put it back together and put it on the road. If you can get to it. Sometimes the engine manufacturers don’t think of the quick fixes.....

 

Have you checked for air in the actual tanks? In the columbia the left tank is actually a baffled tank, with a check valve between the ends. That check valve is notorious for plugging up cause most drivers won't drain the tanks daily like they are supposed to.

 

Get under it and look at the left tank. It will have a drain on both sections, the front and back.

 

Is the discharge line carboned up? Seen some you could barely stick a pocket screwdriver in.

 

Your unloader is fumed up and bypassing most of what you compressor is trying to do. The unloader mounted in the top of the compressor is where you’ll find your problem