99 Buick Century why is it every time it is cold temperatures outside my heat or a/c doesn't blow?

I have to take it to the shop and it was a fuse and a resistor switch on the blow motor. Also sometimes I get in the car while it's turned off and I hear air blowing on high when the car is off and the knobs are turned to off?99 Buick Century why is it every time it is cold temperatures outside my heat or a/c doesn't blow?Have the shop check the systems blower relay..