Craftsman 1 hp 3 gallon air compressor will not go above 45 psi, what could be the problem.

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

If it's new I would return it. However that model number 16638 is for a Huffy Bicycle.

Hi sugarplum10...
Normally the tanks are regulated to about 125lbs psi
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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.

check head gasket

my ace air compressor which is 26 gallon 5 hp will not get over 60psi what is wrong with it please?

sounds like the regulator is faulty, normal running air should reach 110 psi, this will allow you to run tools...

Yes,but if the max is 125 you don't want to increase it above 110 and set off the pressure relief valve.

chech air filters for restrictions if not compressor internal parts worn!!!Good Luck to You!!!!