Odyssey dual a/c problem

hi. My wife's odyssey air con has often lately only been blowing ambient temp air when turned on at the front. But the back always works. We had the dealer look at it but they couldn't find anything wrong - pressures all okay etc. Since getting it back, with a bit of trial and error we have discovered that when the front is not working, if we turn on the rear a/c, the front immediately turns cold and stays cold from then on even if the back is turned off again. Has anyone experienced this problem so we can get it sorted. Odyssey is late 2003 model with 132,000 klms.

Not too sure about the older ones, but the 2012/13 model the rear is all electric, with the compressor and fan located in the rear right quarter panel. It's a completely separate system.

The only thing in common would be the cabin temperature sensor, in the panel below the steering wheel. On mine, it has a temp and humidity sensor, and an air tube going into the main A/C box.