Air conditioning and heater were working fine. All of a sudden the air selection knob stopped working. No matter which selection I choose, the air keeps coming out of the front vents. I set the temperature knob to the hottest setting and it doesn't get hot. Does the hvac unit need to be replaced or just the heater core?

 

maybe your cable popped off, or perhaps something worse. You just need to Open it up and see whats wrong. Its really easy just pull out the knobs, remove the two screws and pry the whole bezel away from the dash using some kind of plastic tool that will not damage your dash. You may be able to just tug on it with your hands depending on how stuck on there it is.

 

If engine temperature comes up to normal as indicated by the coolant temperature gauge heat is available. If not suspect the thermostat.

There are two doors in the heater box each controlled by one of the large heater knobs. The one on the left controls the blend door which mixes warm and cold air to achieve the selected temperature. That may be stuck or the cable may be kinked or broken. The large knob on the right controls where the air goes. It also has a cable that could be stuck or broken.

The only time you would need a heater core is if it is leaking. On old cars I occasionally find the heater core plugged with some DIY fixit leak material that has been placed into the radiator.

 

Thanks guys, I'll check it out this weekend.

 

I hear they break often, better be careful with mine.

 

This is the first time it happend to me through three evo ix, but this is the first evo I've had that has surpassed 100k miles.

 

It is way more common on the VIII, at least in the US, because they didnt even give us a damn in cabin air filter.

 

Retro-fitting the cabin air filter into an 8 is so easy! A utility knife, the filter, a couple of screws (and screwdriver), and about 5 minutes of time and, BAM, you have a cabin air filter.

To the OP: If you really need heat (or in my case the heat for the defroster), you can fairly easily reach under the dash (on the right side near your gas pedal foot) and move the gear for the adjustment by hand.

Many of these things are covered in the HVAC mega thread.

 

Yes I know, and I have, but most wont know anything about it until it breaks. It just seems like such a dumb move on mitsu's part.