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Where oh where has my airflow gone?

17K views 47 replies 10 participants last post by  rojo116 
#1 ·
Hi all, hoping you can help me isolate an issue that has cropped up on my wife's 09 ride. She got the vehicle a few months ago, and loves it, but I'm starting to see why it got traded in when it did. Nothing huge overall, just little stuff so far like the A/C compressor clutch (replaced), stereo pre-sets falling out (fixed), and other such minor issues, but the latest one just has me scratching my head.

After the car's sat for a while, like a few hours, all is well in HVAC land and the cooling and heating do as they should. If, however, the drive lasts for more than 25-30 minutes, the amount of air coming out of the vents of any kind falls away until it's basically not moving even the slightest of breezes. I can hear the blower motor running across the switch range, so it's not on that side of things, and no mode selection seems to change the results. If we park the car and leave it for a while, we'll get airflow back for a length of time relative to the amount of time sat off. This makes me thing that I have an electrical issue that is failing after current flows long enough, and then when everything cools back off again, it's all good for a while. Has anyone seen or dealt with this before? I'm wondering if it's the damper motors in the vent manifold cooking and then failing closed?

Any ideas would be great. I can't get a good enough hold on my hair to pull it out, but I'm about to get creative...
 
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#3 ·
The thing is though that it's not a case of not getting cold air. It's not getting any air at all. It really seems like something is physically restricting the airflow into the cabin. I can't even get ambient temp air to blow in, but the blower is running perfectly fine.
 
#4 ·
It might be freezing up to the point that no air can flow past the evaporator coil,or the thermostat is faulty and shuts down the damper. I'm no A/C expert, I just have a slight bit DIY knowledge on these work. If it is freezing up, try turning on the heater for a few minutes to see if this melts the freeze up and then turn the A/C back on.
 
#8 ·
It's still something that should be checked first when airflow is weak...

The OP mentions the fan running fine, even though there's eventually no airflow over the course a 25-30 minute drive. So I can imagine a lot of nesting material that over the length of a drive compressing up against the filter. And maybe the rodent fluffs it up when the car is sitting?
 
#9 ·
Sounds like the blower motor resistor is on its last leg. Remove the glove compartment and check the blower first with an outside 12v source. Disconnect from the resistor and test. If it runs then its probably the resistor. When there is no air coming out of the front vents after 30 minutes of driving, put it on heat and see if it stays the same. If yes, its most probably the resistor. Another sign is the fan speed maybe stuck in one speed even if you blast it or go minimum.
 
#23 ·
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.
 
#11 ·
I still suggest checking the filter. If it's clogged and wet, who knows if it's not causing a problem that gets worse the longer the blower pulls against it?

If the filter hasn't been changed in the last year, you need to change it anyway.
 
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#14 ·
Hey folks, thanks for chiming in. It's been a messy couple of weeks, so I haven't gotten the chance to do much work on the car (or posting), until yesterday. I did change the cabin air filter, and it was definitely in need. I'm guessing the previous owner hadn't changed it in at least a few years and it was dirty and had all sorts of crud built up in it. I got the housing cleaned out the best I could, and I do think that it's blowing better and colder than it did before, but I'm still getting the low air flow after a while.

As I've thought about it though, I think that the suggestion that the coil is freezing up may have more merit than I gave it credit for. When I checked the freon level before, it was while I was diagnosing a no A/C situation (bad clutch coil), and the system wasn't cycling at all. I'm going to try see what it shows now with everything flowing as it should, assuming I still have light when I get home.

Thanks for the thoughts and suggestions. I'll try to be a little more timely with follow-up as I find things out.
 
#18 ·
Sorry if I was unclear. The blower runs fine across the speed range in accordance with where the switch is set, so I'm fairly convinced that it's not a blower or control/resistor issue in this case. That would have been one of my first thoughts if the blower was failing as I've had to do plenty of resistor pack replacements in other vehicles for just that reason.

Thanks
 
#19 ·
So let me get this right, the blower runs fine on AC and Heat for about 1/2 hour and then just stops blowing after that on both settings? While this no or air or very low air is happening, you can still hear the blower humming loudly when fan speed is set on full blast? On both AC and Heat?
 
#20 ·
So far, it's only on A/C, or auto, which right now is the same thing. We haven't had days that were reasonable to have heat on long enough to see whether it's doing it then as well.

The trend has so far been basically:
Driving with A/C or auto climate on for 20-30 minutes, air flow falls off to the point where it's not notably coming out of the vents at all.
Mode selection makes no difference to the amount of air being moved after it falls off.
Blower motor runs and is responsive to the fan control throughout.
Letting the car sit for an hour or so will generally get air flow back for a while.

A frozen evap coil blocking airflow seems to be a likely candidate. I'm hoping to have a chance to look at it more in depth this weekend.
 
#46 ·
So far, it's only on A/C, or auto, which right now is the same thing. We haven't had days that were reasonable to have heat on long enough to see whether it's doing it then as well.

The trend has so far been basically:
Driving with A/C or auto climate on for 20-30 minutes, air flow falls off to the point where it's not notably coming out of the vents at all.
Mode selection makes no difference to the amount of air being moved after it falls off.
Blower motor runs and is responsive to the fan control throughout.
Letting the car sit for an hour or so will generally get air flow back for a while.

A frozen evap coil blocking airflow seems to be a likely candidate. I'm hoping to have a chance to look at it more in depth this weekend.
any luck? i’ve bought a 2010 nissan murano recently with no a/c and i replaced the a/c clutch and blows cold strong air now! been working great for months but i only drive 25-40mins at a time, with my 4 hour trip yesterday it stopped blowing strong after 1hr but was still cold just not blowing out as if it’s clogged but i checked everything i could filter wise and everything is good.
 
#22 · (Edited)
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...
 
#24 ·
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.
 
#27 ·
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.
 
#28 ·
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.
 
#29 ·
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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