When I have my heater turn on high on my 2015 F150, you can hear the fan blowing, then suddenly there seems to be a door open and the system gets louder, then it will quieten down as if the door opening and closing. Sometimes is only stays loud for a few seconds then quiets down, then it will repeat doing this. Sometimes it only lasts for a few seconds, then quiets down, other times it will do this for a few minutes, then quiets down. Any ideas as to what is going on here?

 

I've noticed the same thing on my truck. It almost seems like they're trying to keep airflow/moisture off something if I had to guess?

It sounds exactly like an air door opening followed by slightly louder airflow noise inside, then close again.

 

Mine does it also.

 

Same here. I assumed that it had to do with a heat threshold being reached, then redirection of airflow.

 

I've also noticed it. I thought it had something to do with coolant vs ambient temps. Maybe automatically switching from recirc to normal?

 

Same here. Pisses me off because I think something isn't right.

 

This is what my dealer sent me as an explanation

 

More than likely the recirc blend door switching from fresh air to recirculating. That or another blend door opening/closing (foot and face open, then switching to foot closed face open) does this only happen with the system set to "auto"?

 

My 2016 does the same thing..its annoying

 

My system is a manually operated system.