Originally Posted by SilverShadow03

You DO NOT need an entire new HVAC unit.

Unless they're currently out of stock, you need the shaft that broke off. You can get one off ebay like I did. Cost me $22.50 shipped.

1 Heater Control Knob - $10 & change (stealership) part number at home, I'll update the part number later. You might not need this if the prongs on the back are still in good shape. Mine broke along with the shaft.
1 MR979515 WIRE $5.44
1 7801A110 HEATER CONTR $16.00 (revised gears)

These last two I purchased from MitsubishiParts.net....charged me $10.95 shipping! Oh well...Russell couldn't do anything about it.

Replacement of the actual broken shaft is a bit tricky. It pops out but there are gears behind it and they have to be remain in the same position or marked accordingly so they go back together exactly the same way. That way you have full temperature range with the new knob. I found out the hard way and went through a trial and error session...and a six pack before getting it just right LOL

I posted this video in the above Mega HVAC thread showing you how to replace the parts I posted above excluding the actual shaft replacement:

How To Video

Hope this helps you out.

Originally Posted by TJs98GT

Going as far as telling someone they DO NOT NEED the box is replaced is a stretch and assumption without being there to diagnose each individual cars needs. There is a really good chance the repair above will work for most people, but ultimately it is not the end all of repairs for every car. These cars do have issues with the heater boxes themselves.

The 05 Evo MR I just picked up is a perfect example. It already has all the updated and revised parts but still has the issue. If you disconnect the cables and try to manually turn the levers on the box by hand its really difficult but can be done, there is no way a small cable is going to provide that much force through the knob.

Unfortunately it looks like I will end up having to replace that whole unit behind the dash unless there is a repair method for whatever is binding up inside.

Originally Posted by barneyb

I sat my favorite beverage on the dash. It toppled when I moved the car. Now my AC switch works about once in twenty tries. HVAC - always something.