Hello everyone. I have a 2001 GMC Yukon XL that is blowing warm air through the front vents. The rear vents are blowing normally and I know that the 2 systems are separate in my truck. I Am trying to figure out if it is a blend door actuator or if it is the evaporator. When I turn the knob from hot to cold, I can hear it switch over and it does change temperature, but it doesn't get cold. Thanks!