Pbr A/c Sensor?

[NZ Phil]

Hi. The self-diagnostic check on my R32 A/C system comes up with -26, indicating a problem with the 'PBR'. The aircon basically runs hot, unless the ambient temp of the day gets up in to the 30's (very occasionally her in NZ!) when it kind of goes 'cool'. I understand the PBR controls the heater flap motor, so if its knackered I guess the heater flap is being held open by this sensor. Does anyone know where this sensor (I suspect its just a resistor of sorts) is located and how to check it? Cheers.