CP7 dewar's vapor pressure value not responding to regulator adjustments -> fully closing (CW) adjustment screw has no effect -> fully opening (CCW) adjustment screw has no effect -> exhaust flow is continuous and not adjustable -> Closed manual valve which is in series with regulator to stop exhaust flow -> used heat gun to thaw exterior of regulator -> opened manual valve and fully closed and fully opened adjustment screw -> no change -> replaced regulator and left adjustment at 0 psi < factory setting < 30 psi -> manually filled CP7 to ~100% using LLCV bypass valve (resulted in CP7 alarm) 

Conclusion: Discovered upon disassembly of removed regulator that it was full of water.  This would have been ice with GN2 flow and explains why the adjustment was prevented as my thawing of the exterior wasn't enough to thaw the regulator's interior.  Otherwise the regulator was normal-no broken or worn-out parts.  The two threaded halves of the regulator assembly don't have and effective water seal between them.  When installed with the adjustment screw pointing up, as this one was, liquid water which condenses on the surface of the regulator during the summer months can enter the interior of the regulator and collect.  I will re-orient any regulators found to have their adjustment screws pointing up such that they point down.  

Expect CP7 alarms over the next day or two as the system comes into a new equilibrium and minor tweaks are made.