When you switch to recycle you should be able to very easily tell the blower motor getting louder as the recycle door opens.
If not, pull glovebox out to let it flop on floor. Look in behind box, the recycle shaft is in there, the actual small motor that works it is to the left, look for wires going to it. Look in the little vents with a flashlight, you should be able to see the recycle door move one way or the other on/off, if not actuator motor is shot or the door where shaft goes into it is stripped. Mine stripped the door shaft hole, I am not going to yank the entire airbox to fix it. I simply made up a 6 inch long hook from coat hanger to go up in the slot and move the door forward or rearward as needed. One way is recycle, gets louder. The other way you need to get heater heat, you don't get it when recycle door is open. I can switch door by hand one way or the other in like 5 seconds.