Had an air con guy out recently as the air con wasn't working properly on this tractor. Tested, re-gassed etc. but still not working. He's suggested calling the dealer as thinks it might be a laptop job to plug in an test/diagnose. By all accounts the temperature switch/dial in the cab doesn't click when it reaches temperature and has advised it "might be the thermal unit". Anything else worth considering before picking up the phone to the dealer?