Mitsubsihi Electric PUHZ-P200

We have an application where there's a PHE installed between compressor and outdoor coil. The PHE is fed with brine of 12°C.
The outdoor is installed in the cellar (indoor) because there was no possibility to install the unit outdoor.
We extract heat in winter for heating and release heat to the brine in summer.
So a second heat exchanger in serial with the standard aircoil.
I realise this is no a common setup;

We have following thermistors 0n the outdoor
TH3: liquid (outlet condensor)
TH4: Discharge
TH6: Second face pipe (halfway condenser) What' the purpose of this sensor.
TH7: Outdoor

Does somebody know what the logic is for determining the speed of the compressor? What ramps up or down the compressor?
What the logic is or determining the speed of the condenser fans?
What the logic is for determining the opening of the EEV?
We now have strange phenomenas where the EEV closes for a TE of - 25°C while in cooling mode and an indoor of almost 30°C.
Is the unit trying to maintain an always fix superheat of +/- 4K?
In heating mode, unit is working perfect.
We only have problems in cooling mode (P6 error = liquid pîpe temperature is lower than -15°C) because te EEV regulates for -25°C. (brine 12C and indoor temperature is 28°C) So superheat is +/- 50K.
When we stop brine flow through PHE (it then becomes very hot in the cellar of course because we're then condensing on the outdoor coil only) then the compressor ramps up and we have a TE of +10°C for an indoor of 30°C. So it's then working fine in some way.

Obviously, the cooling rate of the brine is too big for condensing. We're somehow overcondensing and the thermistor and/or the software are seeing this as an error.

manual page 13 http://www.mitsubi****ech.co.uk/Data...CH424revD).pdf