Hi, I have a Mitsubishi Heavy Industries Split 7.1 Kw heat pump (src71zea-s) which is mis-behaving. It's about 8 years old. I've had the installer out to look at it but after trying to add more refrigerant and much head scratching he left promising to research and return - a few months ago.

Having read several other threads on this forum I have not got any further but figured a question to experts was worth a nudge.

Symtoms
Heat pump seems to run fine with no faults - except inverter does not ramp up in heat mode. Outside unit fan speeds up after start delay but compressor sounds like it is running though never speeds up. Inside unit goes through it's normal starting functions but similarly, fan doesn't speed up from low.

This operation is the same when High power mode is selected.

In cooling mode, the system behaves perfectly with the compressor ramping up and cooling very effectively.

Diagnostic/Service Mode
The unit has never stopped abnormally. When pushed into service mode, there is no stop error code indicated by flashing run/timer LEDs.


I would welcome any suggestions of sensors to check or advice on where to next.

Many thanks