I have a Craftsman air compressor with 25 gal tank, 5.5 HP Model # 919-16523, SN# AC0616. It will not build pressure greater than 20psi. It has worked great until yesterday.

SOURCE: My 5 hp, 25 Gal. Craftsman air compressor is

It sounds like your intake valve is worn or defective. Take the head apart again and look to see if the valve is sealing properly. If you post a comment with your model number I can look up the specific parts at sears parts.

If your compressor is functioning properly, air should not come out of the intake muffler (filter)

Thanks,

Tim

SOURCE: My craftsman 25 gal. 5 hp. compressor builds 120

Replace check valve the piston is getting stuck sometimes alloying the air to leak all the way down till it comes back on

SOURCE: My craftsman air compressor model 919 16737 1.1 hp

Probably the check valve has failed. It apparently is where the pipe goes into the tank from the compressor.

SOURCE: Craftsman 3 gal., 1.5 hp air compressor: won't

The compressor will not auto shut off until it reaches the preset pressure which is usually around 100-130 psi - your problem is leakage of air from the oil filler cap suggesting that you have a failed internal valve.

SOURCE: I have a 3 gal 1 hp model 921-153101 and i was

sounds like a valve broke and you need to replace the valve plate.


http://www.mastertoolrepair.com/sears-craftsman-921153101-p-24902.html?osCsid=ke90vvsu0rof263nthcsf9e9a1