Air Conditioning running coolish the warm

[boeing]

Hi!, I have a 2006 2.1 litre V6 x-type that has done 70,000 km. We are in Western Australia and the summer temp is getting around 41 degrees C. Problem is the drivers side vents (right side) put out coolish to warm air (fluctuates) and the passenger side just puts out warm air. We have had the gas checked and it is fine. The mechanic thinks that it is the blend motor/door but I am not so sure.  There was a technical bulletin about the compressor valve spring so could that be it?

When the temp drops down to around 30 degrees or below it seems to work fine. Speaking to a Jag specialist mechanic he has advised that the air con does not usually cause an issue. I have it booked in for the 15th February for them to have a look at. 

Any assistance would be appreciated.