High pressure shut off valve will not shut unit off when it reaches 100 psi

that's a big unit. Reach out to Atlas Copco technical department direct.

http://originair.atlascopco.com/atlascopconew/contact.aspx

http://originair.atlascopco.com/atlascopconew/industrial/compressors/atlas-copco-ga-45-ff/75ef5d89-fc23-4eca-8c0c-d5a823922470.html

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if it is a 11cfm compressor then it produces 11.8 cfm of air regardless of the pressure
pressure has nothing to do with cfm but with the restriction to air flow
for example the tire inflator -air hawk- has a very small cfm but as the tire restrict the air flow the pressure builds up to set pressure on the gauge
so if you want 100psi from the 11.8cfm unit just adjust the pressure switch to shut off at 100psi
Cfm is only important when using air tools as a compressor that is not capable of maintaining the cfm thereby the pressure to run the tools is not a good idea
as an example
a sand blaster that uses 11.8 cfm at 100 psi will not work on your compressor
that unit will require a 20cfm compressor to run it peoperly

The pressure switch is either out of adjustment or has failed. The compressor should shut off at a much lower pressure than the safety valve (~100 psi)

Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/dave_fb2c45146b845cea

It sounds like your pressure switch is not set correctly. It is possible it is set too high for the compressor you have.

I can not find a Craftsman compressor with that model number anywhere so here are a couple things to look into. If the compressor fills to 70psi and keeps on running check the valve plate and piston/cylinder assemblies. Check that the valve reeds on the valve plate are not bent, broken or warped from heat. Then check that the wiper (oil less) or pistion rings (oil splash) are not damaged and that the cylinder wall is not scarred up. Any of these will let the compressor fill up to the point where the air pressure leaks past the valves or piston and won't fill any further. If the compressor fills to 70psi then shuts off the problem is in the pressure switch. Some have an adjustment screw or bolt to control when it turns on and shuts off. If you had a drop from 100 to 70 the springs may be weak or broke and you'll have to replace the switch.

If your compressor reaches the cut-out pressure (or very close) , most likely not reed valves. Usually air leaking when compressor is shut off is result of leaking check valve at the tank. Look for brass valve and remove. Somtimes the valve is repairable if debris is keeping valve open. Clean or replace as needed.

I assume it keeps pumping, but doesn't build any more pressure. That is probably bad valves or rings. If your unit has a crankcase breather, and it is puffing alot of air, look for rings. Otherwise valves.

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.

check the non-return valves in the pump block. if these are damaged or dirty you pressure will be greatly reduced. they are located behind the 3 lage brass hexagonal caps.

I hope this helps

Replace the pressure valve. It is not sensing the pressure properly and that is why you are having this problem. Why it failed is beyond anyone