Setup one of the liquefiers for Dewar Cooldown Mode:
1.) Incoming flow (FC501A/B) should be as large as it can be. Ideally this should be around 60 slm but whatever the greatest flow is that you can hold consistently.
2.) The outgoing flow (FCA/B) should also be large so that the flow runs into the Coldbox, over the cold heads, then down to the dewar and out. This can be as high as 40 or 50 slm.
3.) The needle valve (NV501A/B) should be open at least one full turn more than the standard position. The standard position is approximately 1/4 turn open.
The cold head temperatures can get warmer in this phase with that not being a problem. The pressure on the dewar can be 6-7 psi and the flow in and out must be consistent. It that is hard to achieve there is usually an issue with the dewar or flow controller. Sometimes the flow controllers will behave better at higher pressure. When cooling at a high rate with the needle valve open the dewar neck will likely cooldown and frost up so its good to have a fan pointing on it to keep the ice from forming too much.