If trying to fix so no overheat...then the 1st tech is correct. If you want a working nav/radio/climate control unit...seek professional help. Sorry but it will also be very expensive. Consider checking all fuses and wiring, and anything that has been done to vehicle recently that could have contributed to this problem like aftermarket radio or componets wiring and such...sometimes something was left un plugged or randome wire cut, or someone tied into a power at the wrong place, or bad grounds...because it is a Jag...it is 3 to 5 years ahead of all none exotics cars as far as technology so you may need a pro shop to help...

As with any car run the car for about 1/2 an hour,or until it is hot.Feel your top radiator hose, if it is hard and you cannot flex it. That is telling you your thermostat is stuck in the closed position and your antifreeze, is not circulating,which would explain your cold air. I hope this helped.