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Ok, I have had this off and on a few times in the last couple weeks. 00 323i. I am driving with the snowflake lit up, temp at 61 with auto recycle on. Upper and middle vents lit up. Suddenly it feels really hot. Ice cold still blowing from front vents... the top vents by the windshield are blowing scalding hot air. If I turn on the floor vents as well, those blow super hot air, but the dash is still blowing cold the whole time. I did a search and others have had similiar problems but noone posts what they did to fix the problem. Middle wheel is on 3 blue dots. I have and have read the owners manual. I have replaced the thermostat and water pump and done a full flush. Car is not running hot. Weird thing is, I turn the car off, and then next time I drive it, it's fine.. no issue. Anyone??
 

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Ok, I have had this off and on a few times in the last couple weeks. 00 323i. I am driving with the snowflake lit up, temp at 61 with auto recycle on. Upper and middle vents lit up. Suddenly it feels really hot. Ice cold still blowing from front vents... the top vents by the windshield are blowing scalding hot air. If I turn on the floor vents as well, those blow super hot air, but the dash is still blowing cold the whole time. I did a search and others have had similiar problems but noone posts what they did to fix the problem. Middle wheel is on 3 blue dots. I have and have read the owners manual. I have replaced the thermostat and water pump and done a full flush. Car is not running hot. Weird thing is, I turn the car off, and then next time I drive it, it's fine.. no issue. Anyone??
Heater control valve is failing/failed. It is the valve that allows hot engine coolant to flow through the heater core in the dash. If it is open when it shouldn't be, it acts EXACTLY like you described - hot on floor and defrost and cold on all front vents. It's the little tin-can looking thing mounted low on the drivers side wheel well in the engine bay. It has two wires connected to it, and there are two hoses coming out the back (that you can't see easily until you get down to it.

That valve is a pretty common failure item in our cars.
 

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A bit late, but my car had the same problem except it was all the time. I changed the heater valve and problem was fixed, so I just wanted to post to let others know that this is a good fix for this problem. Also, you may notice that the defrost and floor don't blow hot air until the car warms up which is the key indicator that it's the heater valve.
 
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