Heater blows all the time

Heater blows all the time, doesn't matter what the setting is on (even in off position) blows hot even when you set it to cold.(Front & rear are doing the same)no response when pressing a/c button either. Seems to be blowing at high speed though

No matter what the selector is on (defrost, floor, vent ect. Even off position)The heater is blowing (seems like high speed) Even if you turn the temp setting to cold still blows hot. The rear heater is doing the same. It's seems like the system is in some kinda bypass mode. Spoke to local dealer & cold Hyundai Teck line, said to try transistor (which I have ordered)I feel this isn't the problem though. This transistor seems to be for fan speed I believe. When I unplug it the fan in front stops but the rear keeps blowing & can't change rear temp. Any help I will appreciate.