2008 Nisson Titan. After 2 hours of highway driving the fan goes full speed with the temp selector not full cold any movement of the fan speed does nothing. Shut the truck off for a minite and all works fine. Or, the fan speed work fine but the air vents don't blow air out. You can hear the fan blowing but no air flow. It's like it's froze up. Turn the truck off for about 1/2 hour and it works fine. Any help!