Hi TerryB,
Sounds like what you have is a frozen spool steam in the regulator.Look on the back of the regulator body and see if there is a nut that can be removed. If so remove it and carefully pull out the spool steam and nut.The spool steam should sit in a tube on the bottom of the nut with a small spring in between them. Gently pull the steam from the tube on the bottom of the nut and and you should see a o-ring.This steam with the help of the spring moves back and forth in the tube and regulates how many air psi is allowed to the working side of the regulator..If its frozen then it will not respond to the control knob.If it is frozen then clean it well and apply a little grease to the o-ring and spool reassemble it and place a little grease on the disc you took out with the big spring under it that should get you going.I don't know what compressor you have so i'm not sure of what regulator you have.Some regulators have no nut on the back so the spool comes out the front of the valve body.Hope this helps.Good luck.
Tinker

I have a Dewalt d55141 Type 1 compressor. Is there a diagram that shows the assembly? I have no nut on the bottom but the knob itself unscrews. There's a large spring and a disc that has an O ring. Under that there's a smaller disc with a spring at the bottom. I'm not sure I'm reasembling it correctly. Does the disc with the O ring go in first and then the big spring or does the big spring go in first and the dis with the O ring sets on top of the spring?

Hi Terry,
The big spring sits right below the regulator adjusting knob.So you would have your a pressure adjusting knob then the spring then the disk.Hope that helps.
Tinker