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Try switching from AC to full blast heat and full blast fan speed when the front vent stops blowing air. See what happens.
 

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Have you experimented with driving with your A/C off for 30 minutes?

If the airflow remains normal, then it may point to the evap coil freezing up and blocking the airflow when your A/C is on...

I'd check you cabin filter again too. You mentioned there was lots of crud and that you did your best to remove all of it. More crud may have found its way through your ductwork clogging your new cabin filter...
 

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I think the MO has no separate blower resistor instead its in the relay. Driver side fuse panel. Look here.....
The resistor you're referring to is more of a fuse. On the Muranos, the fan relay/resistor is integrated into the blower motor itself. A faulty relay can cause loss of fan speed control. The solution is to replace the blower motor. It's a 15-20 minute DIY job with only basic hand tools required.
 

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Also, Amazon and Rock Auto have excellent prices on quality replacement blower motors. They both carry the Four Seasons brand, which has a lifetime warranty, for around $75.
 

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Actually, there are 4 identical relays on that junction box. Switching the rear defrost relay with the blower relay will easily test if the relay is bad or not.
 

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I had a first gen (2004), and now have a second gen (2009). The relays y'all are referring to are more like a fuse. If those relays are bad, the blower motor will not work at all. The fan speed relay is attached to the blower motor itself. If this relay is bad, you may only have one fan speed, or not have high speed, etc.. If the fan speed relay is bad, you have to replace the whole blower motor. I experienced that problem with my '04. Thankfully, the blower motors on both 1st & 2nd gens are easy to access and replace.
 

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Another thing to consider is the temperature sensor for the Automatic Temperature Control. It could be malfunctioning and turning the fan speed down. I've never run across a problem like that though, so that's just a thought.
 

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So you are saying that the video clip showing the blower relay of the first gen 06 murano and the 2010 FSM diagram showing the same relay on the the same area is wrong. And that there is no relay there but its in the blower itself? That does not sound right to me. I think there are relays on both gens and you can have issues on either or both. In your case its your blower that is bad not the relay?
 

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I believe the OP has mentioned a couple of times that the fan sounds like it running just fine across its entire speed range, it's the airflow from the vents that is restricted for some reason after ~30 minutes...
 

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I believe the OP has mentioned a couple of times that the fan sounds like it running just fine across its entire speed range, it's the airflow from the vents that is restricted for some reason after ~30 minutes...

If there is a restriction/blockage of some kind, I tend to think that it will cause it to happen all the time not after 1/2 hour. Since its blowing fine for 30 mins. I am more inclined to think its the relay or blower motor itself. Or even the temp. sensor mentioned above. But, if he is not using the auto control and it still happens then that eliminates the sensor. If he switch to heat when the air stops coming out of the vents, and still no air comes out, then I would say its either the relay or blower. If the blower is truly running and air is being moved, it has to go somewhere if not the front vents. What about the floor or windshield vents?
 

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I agree with you that that air has to have to go somewhere. However, if the cabin filter and/or ductwork is clogging for some unknown reason after 30 minutes, then there is no unrestricted air intake supply for the fan to make go somewhere...

I wonder if the problem persists regardless of the air circulation setting being set to fresh outside air vs recirculated cabin air?

Sure hope the OP comes back, it will be really interesting to know what the problem ends up being.
 

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Discussion Starter #33
Hello all, and welcome to the next episode of "How to burn your brain in 30 minutes". I got a chance to fuss with the MO a bit over the weekend and am just getting more confused.

To answer the recurring question, the blower runs fine and responds to controls throughout the process, regardless of what is coming out of the vents. Relay/fuse/mouse with a hand crank/etc is fine on that end as far as I can tell.

So far, I've had two different additional experiences with it:
  • Friday evening going to the HS football game with a few detours for errands on the way and it happened again. This time, I DID NOT have the A/C on, it was in fresh air mode with just external air and the blower speed stayed constant although the airflow did not. Didn't have time to try and run it hot for a while to possibly defrost, but don't see why it would be a freezer issue at this point anyway.
  • Saturday afternoon trying to diagnose in the driveway. Sat with the car running, full A/C, range of fan speeds, for at least 20-25 minutes, all vent modes tried at some point or another as well as fresh vs recirculated. No loss of air flow at all the entire time.
  • Saturday evening, went for a drive with the wife and noticed loss of air flow about halfway in. Turned the head way up to try and defrost and had no real change by the time we got done (approximately same timeframe). After sitting for an hour, all good once again.
As a conjecture, could the vent door motors be overheating and failing/falling closed at some point?
 

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I don't think there is a vent setting that blocks all airflow that I know of...

You mentioned your test in your driveway did not reproduce the problem, correct? If so, then it may have something to do airflow during driving moving/compressing some material and blocking the vent up...

I keep thinking it's something within your vents that gets compacted after driving a short time, then loosens up when sitting. Bizarre idea I agree, but what else would cause this problem...

What did you find in your cabin air filter and vents when you cleaned it?

You mentioned you cleaned it the best you could, is it possible there's more stuff in there?

There are relatively cheap endoscopes available on Amazon that may allow you a greater view inside the ducts that might be worth trying... However, it can sometimes be difficult to get the endoscope camera to follow turns in the vents...
 

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Discussion Starter #35
For the most part, the cabin air filter was just filthy, although I did find tree seed hulls in the filter face as well. I may try the scope idea, just to try and get some sense of it. Thinking I might pull the blower as well and check the passages from blower to distribution box.
 

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Separately, I have found a leaf, a small acorn in my filter. On my wife's crv I discovered some fiberous type insulation had somehow fallen onto the blower impeller. It wasn't stopping the flow of air but it was making a very unusual sound. It will be interesting to see what you find.

Sent from my SM-G960U using Tapatalk
 

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For the most part, the cabin air filter was just filthy, although I did find tree seed hulls in the filter face as well. I may try the scope idea, just to try and get some sense of it. Thinking I might pull the blower as well and check the passages from blower to distribution box.
That's almost certainly part of the problem. Not a bad idea to get into it a bit deeper if you can.
 
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