Frank,
Welcome to TBN Blue. I second it on what Bill said. With the rate of drop knob closed, you can raise the 3 point, but can not lower it. Additionally you may have some blockage in your spool valve unloading valve. To eliminate ice buildup possibility due to some moisture, I'd get a heat gun or blow drier and put a little heat where the spool valve is. it should not take much to thaw it out if you indeed have moisture.
JC,