2002 Sante Fe heater/AC problem

My Sante Fe has been the best car I have ever owned. I have 138K miles and the only issues I have had have been minor. My current heater/AC problem is intermittent but often the fan does not
blow any air. I can change fan speeds, hear the fan speed faster or slower but no air flows. Could it be related to the defrost setting? It will work for 5-30 minutes, then stop working, then start working again. Same with the A/C. My other issue (unrelated to the heater/AC) is I hear a "whoop" sound intermittently but I can not repeat it intentionally. I can not tell where it is coming from since it is always just a very short sound.
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It'd be very odd for the blower to operate but not move any air. This implies some sort of blockage to the air passage. I'll presume you don't have all the air registers shut.
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Correct, the air registers are open. Air will blow for awhile, then stop for 10 minutes to many hours. Sometimes I will shut it off for 20 minutes and when I restart it might work, might not. I'm trying to find a pattern but have not been successful yet. Closest I can tell it may be related to if the defroster (A/C) is running or just the heater. It seems that something may be freezing over and not allowing an internal door to open -- is that possible? Is there a sensor that might be causing this ?
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Correct, the air registers are open. Air will blow for awhile, then stop for 10 minutes to many hours. Sometimes I will shut it off for 20 minutes and when I restart it might work, might not. I'm trying to find a pattern but have not been successful yet. Closest I can tell it may be related to if the defroster (A/C) is running or just the heater. It seems that something may be freezing over and not allowing an internal door to open -- is that possible? Is there a sensor that might be causing this ?
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Correct, the air registers are open. Air will blow for awhile, then stop for 10 minutes to many hours. Sometimes I will shut it off for 20 minutes and when I restart it might work, might not. I'm trying to find a pattern but have not been successful yet. Closest I can tell it may be related to if the defroster (A/C) is running or just the heater. It seems that something may be freezing over and not allowing an internal door to open -- is that possible? Is there a sensor that might be causing this ?
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That's certainly a possibility. If the evaporator freezes over, the air won't be able to flow through it. There's a thermostat in the evaporator that is intended to shut off the a/c compressor when the evaporator temperature gets too low.
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Where is the evaporator and how do you get to it? I have talked with a Hyundai Service Manager and he said to bring it in when it is not working. It is so sporadic that each time I bring it in it has not failed for the mechanic. Could turning of the defrost/AC help to "unfreeze" the situation and make it work again?
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The evaporator is behind the right side of the dash. You won't be able to get to it without at least partial dash disassembly.
Ask if you can bring the car by when it's not working so someone can at least experience the condition right then. Based on your description, it sounds as if once you drop it off and it gets parked out back for a couple hours, the condition disappears.
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