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Discussion Starter · #1 ·
My 2016 Altima is been occasionally having this issue, but the last few weeks it is every time I get in the car.

Given it is hot, I want full A/C and vents blowing as much air through the vents on the dash pointing at me. And I have "recirculate" air setting.

It works fine and the A/C is cold, but within 1-3 minutes the airflow to the dash vents decreases and more airflow is directed to my feet. I and turn it all off or sometimes cycling through all the modes (windsheild defrost/defrost and floor/dash vents/etc) will fix the issue for a while. And when I say the airflow decreases, it is noticeable (especially when you are sweating away). It is a more significant change to airflow than moving from "recirculate" to "fresh air" modes.

My assumption is that there is a bad servo or something like that in the part that modulates where the airflow goes in the HVAC. I just have no idea where it is or how many curse words will be uttered as I attempt to replace it. And will I give up and bring it to a shop in the end?

Any help would be greatly appreciated.
 

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That sounds like either a bad TXV Valve (stuck open) causing your evap to ice up, or a blocked evap drain causing the evap to work in a water puddle. All incoming air passes through the evap regardless of temp setting, the flow just bypasses the heater core when you're set for cold. So an evap blockage will reduce airflow on any setting. The fact that it works again after being off for a bit indicates the culprit is ice.
 

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Discussion Starter · #3 ·
That sounds like either a bad TXV Valve (stuck open) causing your evap to ice up, or a blocked evap drain causing the evap to work in a water puddle. All incoming air passes through the evap regardless of temp setting, the flow just bypasses the heater core when you're set for cold. So an evap blockage will reduce airflow on any setting. The fact that it works again after being off for a bit indicates the culprit is ice.
Thanks. Would this icing condition occur within 60 seconds sometimes when the car has been sitting in 100 F ambient temperature for more than an hour? I don't know that I have turned the unit off to clear it. I have only cycled through the vent settings slowly between the defrost, defrost and feet, forward vents and feet, then back to full vents. This does lower the fan for a few seconds as each change is made and I do have to move it back to recirculating air due to moving to defrost changes the setting to bring in more outside air.

If the eval drain was plugged, wouldn't I see water eventually spilling into the floorboard when using the A/C for an hour of driving in 90% humidity? That isn't uncommon for me and where I live.

Thanks again for your reply. I am just trying to clarify and give possible evidence that it is this for sure or maybe it is another issue.
 

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Would this icing condition occur within 60 seconds sometimes when the car has been sitting in 100 F ambient temperature for more than an hour? I don't know that I have turned the unit off to clear it. I have only cycled through the vent settings slowly between the defrost, defrost and feet, forward vents and feet, then back to full vents.
No, 60 seconds would be extreme even if the TXV was stuck wide open. Usually you'd be talking at least 5~10 minutes in high-humidity conditions.

If the eval drain was plugged, wouldn't I see water eventually spilling into the floorboard when using the A/C for an hour of driving in 90% humidity? That isn't uncommon for me and where I live.
Yes. But here's the puzzle. The various vent settings can redirect the air but they can't possibly reduce the flow. There are only five things which can do that. A blocked cowl inlet or plugged cabin filter would send the fan into hyperspeed but not move any air, like putting your hand over the hose on your vacuum cleaner. You don't mention the fan going nuts. Then there's a blower motor that's heating up, causing it to slow down until it cools off. You also don't mention an audible drop in fan speed. The remaining two are a blocked evap or a flooded one. No other factors can result in an overall reduction of airflow.
 

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Discussion Starter · #5 ·
VStar650CL - thanks for your input.

I do need to clarify. The overall airflow isn't changing. I want the air to be blowing all in my face to try and stop the sweating. The issue is after working fine for just a minute or two and then a portion (maybe less than 50%) air start flowing to my feet and the forward facing vents have much less air coming through them.

I assume there is some sort of diverters that move doors that directs the air between the defrost, floorboards, and front vents and that is messing up.

I don't know if this is a "take it into a shop unless you want to rip about 1/2 your dashboard out to find and replace the parts".

Thanks in advance for anybody that can shed some light on the issue.
 

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If it's an Auto A/C system then it will divert the airflow according to the cabin temperature and the set temperature when the controls are set on Auto, but generally with a hot cabin and a cold setting it should stay on "face". So if that's happening in hot cabin conditions or happening when the Auto light is out, then I'd say your HVAC control head (Nissan calls it an "AC Auto Amp") has an issue. The HVAC is on the CANbus on gen5 Altimas with Auto A/C, so getting it scanned may tell you something. The servos on both Auto and Manual setups are under control of the HVAC and don't do anything without being told, so I doubt anything except the computer in the control head could cause that sort of misbehavior.
 
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