HVAC Air Flow?

[Honcho]

Now that the weather is warming up, I'm using the HVAC more often and I noticed something. When I have the car set to fresh air intake, even the max blower setting results in a fairly weak stream of air. However, when I set it to recirculate, it blows strong. I can't remember if my 91 was like this, but is this normal?

I'm wondering if my cabin air filter is restricting flow...

 

[RYU]

mine is the same but i'm also running a cabin filter. in my other cars this is pretty normal IIRC. I just tested it in my Tesla and RECIRC is stronger.

 

[Kaz-kzukNA1]

Hi, Honcho.
That’s quite normal and in fact, it should behave like that.

When in fresh mode, the fan motor is pushing the fresh air from outside into the cabin.
The air inside the cabin must first escape through the multiple vents before the fresh air can replace the existing space/volume.

On the other hand, in re-circ mode, the motor is just re-circulating the cabin air.
No need for ventilation and thus, less friction.

Kaz

 

[Superhatch]

As someone who has to use a balance of fresh/recirc when it's -40 out, can confirm recirc is always stronger.

The question is should fresh be that weak. That I'm not sure of. If you have AC off/fresh is it stronger?

 

[Honcho]

Hi, Honcho.
That’s quite normal and in fact, it should behave like that.

When in fresh mode, the fan motor is pushing the fresh air from outside into the cabin.
The air inside the cabin must first escape through the multiple vents before the fresh air can replace the existing space/volume.

On the other hand, in re-circ mode, the motor is just re-circulating the cabin air.
No need for ventilation and thus, less friction.

Kaz

mine is the same but i'm also running a cabin filter. in my other cars this is pretty normal IIRC. I just tested it in my Tesla and RECIRC is stronger.

Thanks guys. I suppose the fact that I have all new door and body seals only makes it more difficult for the air to escape. I thought perhaps the vent recirc door was not opening in the blower, but I can hear it running.

 

[bullithollywood]

If youre using a HEPA cabin filter over the external fresh air inlet its cutting your flow by about half. Pull it and youll see.

 

[Wild Turkey]

If you're using a HEPA cabin filter over the external fresh air inlet its cutting your flow by about half. Pull it and youll see.

Hmmm. Maybe I should check my filter since I don't think the rest of my setup provides much filtration anyway in the configuration I usually run (windows and targa roof open). The filter didn't seem to provide much resistance to blowing through it, but I'm running the Fram CA9115, not HEPA. I'm going to test it again. When I originally threw it in, I didn't notice a difference, and it just dropped in with no cutting, brackets, whatever.

 

[Honcho]

Hmmm. Maybe I should pull my filter since I don't think the rest of my setup provides much filtration anyway in the configuration I usually run (windows and targa roof open). I'm surprised since the filter didn't seem to provide much resistance to blowing through it, but I'm running the Fram CA9115, which is not HEPA.

I'm gonna pull mine as well just to see the difference in flow. If it's restricting, I may adapt the 3D printed brackets to include a basket for a less restrictive fiberglass filter like the cheap ones for your furnace. It's really about keeping the big particles and trash out of the blower/evap. HEPA is probably way overkill. You can buy a single furnace filter and cut out like 10 NSX filters from it.