heater blower is weak
 

started out fine, had the heat cranked up to 4 then a mile into my trip it felt like it had hardly any air coming out at all and the blower got quite. Got to where work shut the truck off and restarted it. What's going on? If it's some safty thing that the blower shuts down when it can't suck in enough air where do I look for the intake of it?

Intake for when on fresh air mode is under your windshield cowl, recirculation mode intake is passenger floor upper kick area.

If the fan stops working on certain speeds or isn't as powerful its most likely the heater blower resistor which controls the speed of the blower motor, or the blower motor is dying. Both are usually replaced if the motor is dying.

If your still under your warranty best to take it back and have them check it

If you have the temp. in your truck set to a specific # once the cab reaches that temp doesn't the fan slow down until it needs to speed up again to return to the preset temp?

The fan speed varies in mine from time to time depending on the temp. I set. I thought that was how it worked.

I am not, well since you mention that it's under the cowl, we did have a light snow that all blew up into that area all at once. Maybe that caused it?

I experienced something similar to this in my 2011 a couple of years back. Took it in, and they said something in the heater electronics had failed, replaced under warranty and was good to go for the next couple of years till I traded it in on my 13.