why is my climate control working by itself?

There is definitely something amiss with your automatic climate control. It would be best to have someone scan your climate control computer ( and do a full systems scan ). This should help solve the mystery. It sounds like the controller is staying on when it should not. By scanning the data stream for the climate control you can see if there is any contradicting information. I have replaced a few climate control computers on 740s so it is not rare to have issues with these systems or their controllers.