Came in this morning to find the helium return line to the buffer tank 
frosted up. MV51 has been stuck open the whole time. That exlains the 
cooldown rate and other problem. Cycled MV51 a few times and it now seems 
closed. Switched back to parallel cold return this moring at 8:00. Rates 
are much better. The E-log was also down this morning.