UPDATE: Issue found

See heater core dissection:


For those of you following my garage thread for Swarthy, you know that I have a bit of a HVAC heat issue. I get warm / hot air out of the driver's side vents, but cool or cold air out of the passenger side vents.

I noticed the issue on the 2 hour drive home from getting the car. The car simply did not get overly warm in the cabin. On the test drive everything seemed okay. Spork also confirmed this as she went with me to get the car.

On this morning's trip in to work, I did a bit more testing of this. I found out that it simply does not blow hot air with the fan blasting. It does blow warm, but not hot. This is despite the engine coolant being fully up to temperature (180F+). The driver's side is a lot warmer than the passenger side, but still not as hot as it should be IMO. It is noticeably cooler than any other car I've owned.

I also tested the temperature out of not only the normal vents, but the defroster vent and also the floor / feet vents. The same thing happens. The driver's side blows much warmer air than the passenger side.

I had a suggestion from Eggman to check to see if the cabin air filter was at fault. I did this and noticed it had probably never been changed. I cleaned it up as best I could and reinstalled it into the car. It definitely was dirty and needs replacing, but it is not fully clogged at all. Unfortunately, cleaning the filter out did nothing to fix the issue.

At this point, I am thinking I have a busted flapper door, a bad stepper motor that isn't actuating a flapper door properly, or something is jammed in there stopping a flapper door from shutting correctly. It seems like some or a lot of cold air is coming in and mixing with the heated air from the heater core. I'm not sure why most of the cold air is going to the passenger side, but that seems to be the case. I'll be looking through the service manual to see what needs to be taken apart to start getting to the bottom of this. Any info, tips, or ideas are quite welcome!