Primary air tank won't build air

[Waterloo]

Im thinking soot build up in the lines along with the unloader like in2 stated. Another thing, there is a head kit for these compressors, as the unit itself rarely fails. So don't get talked into replacing the entire compressor if that is the issue. The head kit is roughly $500 and is something you can do yourself. But, I would still get a spray bottle and spray, spray, spray. I'm always chasing leaks on my ProStar. You think it is fixed and another pops up.