If Nick T. or Jack L. is reading this, we are looking for the same answer.
My son has a 2008 Subaru Impreza WRX with an odd heating problem. My understanding is that the dashboard has 4 vents - one on each end that are non-adjustable/closable, and two in the center that are adjustable/closable. Recently, the car has been blowing cold air out of each end and the drivers side middle vent, but the passenger side middle vent is hot air. I believe floor vents are cold as well. Thermostat is okay, coolant level is good. At one point during a test drive when the car made it to operating temperature on the highway, all vents briefly blew hot air, then it reverted back to only the passenger middle vent only.
Any suggestions for this one? It seems impossible. I believe that the heater core itself is closest to the working vent, but I have no idea about the mechanics of this. In the past, I have had issues like this when the linkage came off the actuator door/flap thing or there was a vacuum line off. But I am at a loss as to why there would be cold air everywhere except that one vent. I do not even know if these doors still vacuum controlled or if they are electric nowadays.
Thank you in advance....