How do take apart a cp7120 pneumatic chisel/needle scaler? Trying to figure out why it doesn't hammer under 90 psi or higher air pressure.

SOURCE: air compressor can't start (hums) under pressure

maybe high pressure vavle is bad

SOURCE: Air compressor motor stalls under pressure

this sounds like a bad pressure switch.if the unit is not shutting off at the same pressure each time this would be the cause.2 if the pressure is not unloading the air pressure on the compressor side of the unit it will cause the unit to struggle when it starts a cycle because the piston is under a load .how this works is say the unit starts from 0 psi when it get to the desired pressure you have it set on the unit kicks off . the other adjustment most units have on them is what pressure to cycle back on.so when the unit reaches say 100 pounds ,it kicks off and bleeds the air off the compressor side so when it starts back up it wont start up with pressure on the piston.

SOURCE: kobalt air compressor will not go above 80PSI

if this is an older or much used unit, cylinder/piston may be worn, unable to push higher psi, which would explain no leaks. if newer unit, seems like regulator unit/valve faulty

SOURCE: I have a Sullair 185 air compressor. The engine

your not return balve is stuck open or your valves are sticking the pressure from the tank is going back to the pump so when the compressor goes on the compress stroke its very hard as it has to open the valve with pressure behind it its hard to explaing buddy but on the tank you wil see anon return valve from the pump unscrew it and inside is a rubber with a spring turn the rubber around and try this if doesnt work you need to inspect the valves (if sticking) good luck

SOURCE: Hitachi EC 12 Air Compressor does not keep pressure

to repair this problem (a) the pressure switch is not working,(b) check valve or non return valve sticking(stripe down repair and refit)