Weird System Behaviour - looking for thoughts (preferably from professionals)
Hi,
Had a Panasonic multi split fitted in October 2025. Outdoor unit is an 8kW 4 way, and 3 units inside (5/2.5/2kW respectively).
When it was first fitted, I raised that the outdoor unit was a bit noisy. I also calculated that the pipe run was 4m over the minimum, requiring 80g of additional R32.
The summer came and during the high heat at the end of June, the system shut down with an F91 error (low pressure). The system was diagnosed as low on R32 and 550g was added (engineer determined this based on the pressure read out.
After this, the system ran great all through July, barely pulling above 800w even when the temperature pushed into the low 30s.
On the 12/13/14th of August, when it was very hot, the system pulled a bit more - 1-2kW throughout the day, which was expected. It kept the house cool.
My concern comes from the behaviour AFTER. From the 15th onwards, the system is now incredibly over-reactive. It turn on my PC and play some games (up to 800w load in the 5kW room), the outdoor unit ramps up to over 1kW. Lower the set point in the bedroom (2.5kW unit) by 1c, system ramps up to 1kW for an hour.
It also feels like it's prioritising either the 2 smaller units OR the bigger unit. Until recently it was happily balancing all 3.
Is it likely that there's a leak / lack of refrigerant again or is this something else? I did read somewhere that the very hot weather can cause the system to adapt its behaviour, which may explain the spiking, but I don't feel like it explains the unbalanced cooling.