Land Rover Repair: 2003 Range Rover HSE Climate Control, range rover hse, 2003 range rover hse

Question
I purchased my RR in December 2010.  Within the first month an annoying squeak started; it seemed to be coming from the top of the dash in the middle.  I took it to the Land Rover dealer for service and asked them to look into it.  He removed the dash panel, adjusted a fan belt, lubricated some things, etc.  All was fine for a few days then it started again.  My car returned for another service, and I had him recheck everything...nothing unusual.  We took the car from WA to NV on a road trip.  For the first 3 hours the squealing was there...then all of the sudden it stopped and has never come back...BUT since then we have had an issue with the temperature coming from the vents.  This started as soon as the "noise" went away.  I had the climate control set to AUTO at 72 degrees and it was blowing ice cold air...the outside temp was 32 degrees.  I had to wear my sweatshirt and use my heated seats to keep warm.  The only way I could get heat was to turn it to 84.  This happened during the daytime...that night, still on the road it started working fine again.  It is three months later and the issue continues.  The installed a new ECU, but it did not seem to make a difference so they took it out.  I have a test ECU in right now, but the issue continues.  Sometimes it seems that sunlight has something to do with it.  One day we were driving by the LR dealer while it was sunny, but cold outside...around 45 degrees.  Since they could not duplicate the problem I pulled in to show them the cold air...I pulled into the garage and the heater kicked on.

I think you get the point.  Any ideas?  Solar sensor??  Broken fan or interior temp sensor?  Any ideas would be great.  I am planning on replacing the solar sensor, but would prefer to not if that is not the problem.  The Rover service guys are clueless: they want an answer as much as I do.

THANK YOU!!

Answer
Any of the temperature sensors could cause that problem, the sun sensor being one of them.  You have sensors for outside air, in car air, and the temps of pieces in the system itself.  It may be necessary for someone to drive the car with the test system hooked up and showing live data.  When it screws up, look to see what readings are off.   Lots of times dealer tech don't want to invest the time to solve a problem like this but there may be no fast way to an answer.  

You can change the sensors rather than doing actual diagnosis, and if you get lucky you will get a fix.  The danger with that approach is that the problem may be a wiring fault, which parts swapping will never cure