My craftsman air compressor model 919 16737 1.1 hp 17 gal 150 psi won't build up any air pressure. It runs but sounds a little odd.

Sounds like the reed valves in the head failed. you need to replace the head (usually cheaper to get a new compressor)

The problem with compressors not building pressure is usually a bad pressure switch or bad regulator. Does the motor shut off at 20psi or does it continue running and not build pressure? If the motor continues to run with no increase in pressure, the you should go over the machine looking for air leaks from your regulator back all the way to the motor. Any air leak while the compressor is running can cause the pressure to "peak" way before the intended shutoff that it is regulated to.

A piston in any engine should be around 100 psi I would guess. A Chevy 350 used to be around 150 psi. An air compressor that only pumps enough air to reach 20psi is obviously too low on compression. Nailers and the like need 80 or more psi. The intake valves may be shot, the unloader might be stuck or piston rings are worn.

sounds like the pressure switch is faulty. not uncommon on compressors anymore.

worn out pump on the compressor, or leak in tank.

could be a gaskit or the inlet reed

Does it shut off at 25 psi or just keep running and never build more pressure than that? Also, did this come on gradually or suddenly? Also, was it being used regularly when it happened or had it been sitting for a while?

The compressor valve may have a faulty gasket or seal, and maybe leaking air internally. Or the compressor might be going downhill. You can try to replace the valve seal and see if that makes a difference, otherwise you need to replace the compressor.

compressor will not build pressure

My air compressor builds up to 40 psi and just keeps running, i have a craftsman 5 GAL, 1HP, 125 PSI and pressure goes up to 40 psi and dose not go any higher and on the other hand engine keeps running and dose not stop. Please advise?
Thanks.
Kia