Split system only dropping 2c then outdoor unit turns off

[scoobydo]

Ok you are going to all laugh but it is a B&Q system (easyfit) been in for many years. I have 3 of these so can swap PCB's etc. It is the AF9 model so corner mount looks like a bit like a speaker if anyone familiar with it?

So what happens is when you first call for cooling the unit stays on for around 7 minutes achieving a 2c drop according to the display on the front of the indoor unit. At this point the relay clicks and the compressor switches off. Then you get a delay and the cycle continues albeit subsequent cooling cycles are much shorter and it appears like there is a hysteresis of 1 deg C.

So it looks like comms is ok between indoor and outdoor unit. Have took the outdoor unit cover off and there is no logic board or PCB present. Yet to take indoor unit apart but guess this is where the logic board is. Included are the pics of what is in the outdoor unit.

Are these symptoms likely to be a low refrigerant level or logic issue such as thermistor mis reporting?

Any help much appreciated, such as service manual so I can check thermistor ranges etc.