How to charge exactly small amount of refrigerant into ultra low temperature freezer?

[gesi]

Hi Expert Guys,
I have BScience ULT 100l. First stage R290 0,12kg. Second stage - they write - R1150 0,029kg+0,056kg. Freezer have 2 comressors SC18CNX.2.
It is very sensitive freezer for ambient temperature.
1. Do you know why they write two amounts in second stage? It is charging in two steps?
2. How they charging this stage exactly 0,029kg R1150? Is there any special weight or other?
3. How they calculate cooling capacity of SC188CNX.2 @ -96C to achieve -86C in the chamber?



Regards from PL

[Brian_UK]

The two weights may may be the possible range of maximum charge allowed.. start at lower figure but do not exceed higher figure.

And stages are often,/normally charged on pressure not weight. The manufacturer should be able to provide this figure.

Came across this document which may be of interest, sorry not metric units.

https://www.google.com/url?sa=t&sour...C2chNEBj4BCBQL

[gesi]

Thank you. I ask you because I was thinking that my ULF have a leakage. BScience send me parameter for update. I do it and ULF now have -80C.

[Brian_UK]

Good news, thanks for the update.

[gesi]

Cause of problems with irregular course of temperature was firmware for first time, and PCB boards from panel for second time. Resized_20210301_073546.jpg Resized_20210301_073539.jpeg
I don't have to make any works with refrigerant.

[Brian_UK]

Sometimes the controls are too clever for their won good...