We bought a Panasonic split system inverter air conditioner (7.4kw) brand new over Christmas so it is only a couple of months old. We had it installed by a qualified air conditioner installer and everything works perfectly as it should. However we have noticed recently that when the air conditioner is off the outside unit remains on continuously. It makes a quiet noise like a fridge/freezer and the fan is rotating very slowly. I'm guessing it might just be cooling itself down as it is currently the middle of summer where I live but would like to know if this is something to expect before calling out an engineer to inspect it.

Contact the installer who installed this unit and have him come and look at it as it should still be under some sort of warranty. Don't try and fix it yourself or call out another party to look at it.

Are you sure the system is "off"? Some of the new inverter-driven systems actually modulate operation to match the load without really turning off. If you are setting the control to the "off" position and the unit continues to run, call your installer to address the problem.

Thanks for the suggestions. I've already called the installer this morning. He's mentioned to keep an eye on it and let him know during the week and he thinks it might just be part of the units cooling action. In the meantime, I've sent Panasonic an email to check and see if it is something that is particular to the type of machine itself and I'm made sure that there is nothing around the outside unit which might be blocking any airflow, in or out. I'll let you know how I go.

All seems sorted. I spoke directly with Panasonic who referred me to a service centre who I've just called. The service centre confirmed that the PC board in the outside unit is faulty and needs replacing and it looks like it might have been due to a batch of faulty machines as Panasonic had notified their service centres. All done. Thanks.