Haj all there, refrigeration-engineers,

I've installed a freezer of +-30m³ for the european commission which has to reach -70°c. We can only reach a temperature of -65,8°c. This cell is placed in another freezing cell of -20°c We cannot find out where the problem lies but when we put of the cooling system of the -70 cell we get a temperature rise of +-10°c in +-1 hour.
Is this normal?
We also think that the compressor have not enough power to freeze the cell down? Can somebody help? I will be happy to send someone the whole story because we believe we've got a lot of problems with this cells.

TNX