You plug it in, or turn it on, and the compressors runs but there is no pressure built. If this is the case with your air compressor, there are a few things to check.
The air compressor may be building pressure, or trying to, but it cannot due to a major leak on the compressor. One thing to check right away is the tank drain valve. If you leave your compressor tank drain open between compressor uses, as many folks do, make sure that the tank drain is closed before the compressor is started. Otherwise, air will drain out of the tank as fast as it goes in and you have a compressor that runs but there is no pressure built.
If there is an air line plugged into the coupler of the compressor, what’s on the other end of the air line? It is possible that an air tool or blow gun or some such is open and bleeding air out as fast as the compressor pump can compress it.
Often it’s the compressor pump that’s the problem
If could be a massive leak that is the reason why the air compressor runs but there is no pressure. But not typically. It’s the pump that’s the problem most of the time.
If an air compressor is running, and there is no pressure being built in the tank, and there are no major leaks, then it’s time to check the following:
Air exiting through intake valve?
While the pump is running, is there air blowing out of the pump intake? Whether that’s consistent or intermittent, if air is coming out of the intake, it’s a pretty sure sign that the valve or valves in the pump head are failing and it is time to tear down the pump and have a look. You may want to look for a rebuild kit for the make and model of compressor, as valves may be just part of the kit.
Pump piston rings failing?
The rebuild kit may also contain piston rings. Besides the fact that the compressor runs and no pressure is built, another indicator of piston ring failure is air blowing out of the oil fill tube.
If there is a serious piston ring failure, not only will there be air exiting the oil fill tube, quite likely there will be oil too, particularly if the sump is full.
Air coming out of the oil fill tube, whether a little or a lot, means that there is piston ring failure. A tear down is necessary, and when doing so, make sure the inside of the cylinder is inspected to make sure it’s not been damaged by metal-to-metal contact as the piston cycled with worn rings.
No air coming out of the intake port or out of the oil fill tube?
Consider the pump gaskets!
At the top inside of many air compressor pumps, along with valves or valve plates, there are gaskets. Depending on the pump, there may be one, two or many, all different shapes and sizes.
These gaskets are there to ensure that intake air stays on the low pressure side of the pump until it cycles, and then drives that air into the tank via the high pressure valve.
Over time, particularly with cheap, import compressors with questionable fit and finish inside the pump, a section of the gasket will let go. It may occur when the compressor is starting, or it may manifest itself when the compressor reaches a certain tank pressure, and the increasing force on the gaskets causes a breach. When that happens, air cycles back and forth inside the pump, but doesn’t get driven into the tank. The air compressor runs, but does not build any air.
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.
Once again, it’s time to tear down the pump.
Your air compressor runs but there is not air built up in the tank? That being the case, I sincerely hope that when you Google a pump rebuild kit for your compressor make and model that you find one that’s not price prohibitive and, upon receipt, take apart and rebuild the pump with good success.