Ok weird thing happened but on my heat it worked. Then I put on my ac/defroster windows started to fog stayed on hot air then all of a sudden went to cold air now won't turn hot. Every speed works just no heat will come out like I said it worked then just stopped. Will that be the Heater Blower Motor Resistor or do you think the Heater core is broken. If any help with the A/C every speed works with that to.