On we started the Liquefier A after cleaning up the Dewar A level sensors using the procedure (docdb). According to the procedure, the bottom tube did not vent gHe on when the coldhead cold head temperatures are slightly above 240 K. So, we had to wait until all the coldheads cold heads are above 272K.
Since then (03/06/2023), Dewar A wasn't producing liquid until the 03/19/2023 afternoon. Below is the log of things that we did.
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Dewar Cooldown Mode:
Historically we have had more trouble with cooling Dewar A down than Dewar B. Dewar A has taken more than 3 days in the past and this most recent time (March '23) its taken about two weeks. This is likely just because the settings were not optimized for cooling and we had better pay more attention to the system setting for switching between production and cooling modes. If the pressure in the dewar is greater than that on the cold heads the dewar will never cool and the system enters a perpetual state where the cold heads are cold but the dewar is warm.
It seems that the green-handled regulator on the QT manifold should not be open too much. This will make the MFC letting in the helium to the cold heads fluctuated a lot which is not optimal for cooling. During cooldown mode you want a large flow running in and out of the dewar with the goal of around 60 slm going in and 24 slm going out. In order for this to work the pressure in the cold heads much stay slightly above the dewar pressure so flow continuously runs to the dewar to cool things down. The black-handled needle valve should be open a lot (maybe all the way) to keep the flow through this area as high as possible. This will lead to lots of frost and ice build up on the dewar neck. This should not be a problem but should be checked and defrosted regularly. When everything is set appropriately the accumulation of liquid should happen in about 24 hours.