Subcritical setup, R134a/CO2 VIAA BPHE.
At standstill, a CO2 can face excessive high pressure when ambient rises.
Therefore, a separate small cooling unit (power by a small generator) is connected to a coil, submerged in the CO2 liquid receiver. This maintains a safe pressure < 40 bar.

But, I have now the following idea. The CO2 flows out of the BPHE, kept by the 134a at -10°C. If we're sure we keep the BPHE always at -10°C, even at CO2 standstill, then we have just above the receiver a point which can reduce excessive pressure without a separate unit.

Am I correct?