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Discussion Starter #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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Discussion Starter #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.
 

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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.
 

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Have you checked your cabin air filter?

Rodents can sometimes make nests in the duct...
 

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Have you checked your cabin air filter?

Rodents can sometimes make nests in the duct...
That was exactly what I was going to suggest. Also, if your refrigerant is low, AC systems may be prone to icing up.
 

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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?
 

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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.
 

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I think the MO has no separate blower resistor instead its in the relay. Driver side fuse panel. Look here.....
 

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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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Discussion Starter #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.
 

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Discussion Starter #16
Still around, just massively short on free time these days. Here's hoping the upcoming job interview leads to better times and better balance.
 

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The amount of AC refrigerant or lack there of or even the coolant level has nothing to do with the fan speed going slower on its own - without you adjusting it.
 

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Discussion Starter #18
The amount of AC refrigerant or lack there of or even the coolant level has nothing to do with the fan speed going slower on its own - without you adjusting it.
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
 

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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?
 

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Discussion Starter #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.
 
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