Luckily there are a few things you can check that will help you determine why your air compressor won’t fill the tank all the way. Check the Intake and the Pressure Valves The intake valve is the mechanism on a reciprocating air compressor that allows air into the chamber when the piston is pulling downward. Air Compressor: Won't build tank pressure. I tightened all of the bolts. Still had the problem. Another spot to check carefully is the unloader valve. I replaced the pressure switch and regulator. Tighten loose air tube fittings to prevent air leaks. the hose gauge is hooked to a relief valve. I have a 12 gal Husky air compressor that i bought from a friend still fairly new. I picked up a free HUSKY 20 gallon air compressor. Shut the drain valve at the bottom of the tank if it's open. that only builds 30 PSI of pressure. There may be some buildup of air in the compressor, or it may not have any air at all. I checked the cylinder head and found one of the bolts loose. Husky Air Scout won’t build pressure by: Bill “Compressor ran but wouldn’t reach 115psi.” OK. That you were changing air nailer sizes shouldn’t have anything to do with this. If the pressure in the compressor tank is dropping and nothing is using air the leak may be bleeding off enough air that the compressor can’t build tank pressure past a certain point. I have a Craftsman Model 919.167242 air compressor. Or, when an air compressor will not stop, it could also signal a major safety concern, and should be addressed immediately, before using the compressor again. It would run and build pressure but never shut off. In some cases, a compressor will run as though it is functioning properly when, in reality, there is a problem with compressor pressure. FREE air compressor does not build more than 30 PSI of pressure?? I checked piston ring and everything looks good. Compressor Will Not Build Pressure. The air pressure won't build above 30 psi, but, the motor continues to run. well the relief valve got stripped out and wouldn't stay opened so i took it off and hooked the hose to the tank pressure. Need help replacing the Pressure Switch (Part n003307sv) in your Porter Cable Air Compressor? The pressure should build to 135 psi and the motor should automatically sh … read more just bypassed the hose valve pretty much and now it won't build and pressure. it has two pressure gauges, one for the tank and one for the hose. The air compressor runs, but does not build any air. Once again, it’s time to tear down the pump. I have a 2 hp, 6 gallon, Bostitch air compressor. When an air compressor will not stop it could signal a problem with how the air compressor is pumping air into the compressor air tank. If the symptoms related earlier about air exiting the oil fill tube or intake port is not happening on a compressor, yet the compressor continues to run with no build up of pressure, then it’s likely that there is a pump gasket failure. Check for air tank leaks and replace the tank if it's leaking. It is likely (I think) just coincidence. What you are checking for is an air leak that you won’t be able to hear when the compressor is running.