Hey there I have a 1999 379. I bought a new air compressor and new Dryer for it. Because it was poping the check valve It would build presser but it would sound like boiling water under the hood. And its still doing it so i checked everything over again but still doing it. Air presser drops to 90psi then starts building again but it well pop untell it reaches 120psi and. the valve that keeps poping off is the 220 psi valve in the side of the Air compressor. I have taken this to 3 shops all they do is Try to get me to buy another air compressor. Well we put this on another 1999 379 today no problems at all. Thanks For looking Any help would be greatly appreciated. To get me rolling again.
Check all the air tanks for blockage also check the braided line right off the compressor for carbon build up I would also check the line back from the tank to the compressor to shut the compressor off I'm sorry I'm having a brainfart and can't think of the name did you check the unloader
Build up the air, let the truck sit, then open the wet tank drain ####. If its empty it's the check valve in the air drier. I can almost guarantee it especially if you have a system saver drier.
Did you find the problem? If not, start unhooking lines. First undo the compressor to dryer line at the dryer. If it still pops off the relief valve at the compressor, that line is blocked. It's not the unloader valves, they are for shutting the compressor off when system pressure is reached.
