Hi,i´m a service engeneer and my company selling Sanyo,Panasonic biomedical instruments.
freezers,incubator,climatc chambres etc...
We do not do fix refridge units yourself, we ordering this work from local refridgeration repair companies.
But i think they do not have much experiens here with cascade systems ,so I need little bit help.
I think they did something wrong.
Everything started in one day the low stage compressor burned out,there was shorcut in coils.
I ordered from factory a new compressor,original was Sanyo C-D110E51 but it was replaced with Toshiba compressor, i can check the model if it necessary, and local company replaced it.
But i think not correctly:
Freezer control electronics works: first starts running a high stage compressor, cascade condenser has a temperature sensor, when -34 C is reached then Low stage switching on and should run until the chamber temperature is reached, then low stage starts switching on/off for holding the temperature in chamber, high stage running 24/7.
High stage should make -34C in 20min, but it takes 30-40min.
When the low stage switching on, then cascade temperature (-34C) starts increase, and when it increases to -12C, that is an error for electronics and it switching low stage off, so freezer will never get the chamber temperature.
Also what i heard, is like oil babbles moving in sytem and the low stage compressor does not stop normally, it stops immediately, bump...
factory recommend refridgerants: H R407D 483g n-pentane 52cc, L R508 260g n-pentane 58ccI I see from invoice,which they but in: r134a 100g, r-407c 500g, r508 350g
What can be wrong? What is the correct procedure when changing the low stage compressor.
I would very thankful for any help!

Freezer diagram is heare:
MDF52_.JPG