The air is coming out of the filter instead of intake . Craftsman Air Compressor 12-gal 1hp model 921.166400

if shuts down at 20 psi regulator is set wrong
it runs but only builds 20 psi, compressor is probably worn out

Could be, do you have a capacitor checker? It sounds like you have a compressor locked up. Do you have oil in the compressor? If the compressor is new I would take it back and see if it is still under warranty. before I did any thing to it.....

could be a gaskit or the inlet reed

use 6 point box end wrench

if they are oilless compressors then the rings are worn

Try emptying the tanks completely. There should be a bleeder valve for each tank. Sometimes after sitting for a while with pressure, the compressor won't have enough power to start. If you get the same response with empty tanks, there is a problem with the pump pistons.

Dan

look at he check valve

sounds like reed valves are bad,sometimes you can take the reed valves and flip them over for short fix,best to put new one in unit.

I would say that the gauge needs to be replaced. These are common items so go to any auto parts or craftsman hardware store and purchase a replacement.

be sure to use some joint compound or teflon tape on the threads so u dont have any leaks.

please rate my answer. thanks.

you should be able to find the manual online if it's available if not Sears would I'm sure be able to tell you.