hey guys, I have a 98 blazer, had a/c work done on it over the summer. A/c works fine, heat works fine, but recently the fan started to make a low pitch, low frequency noise. like "thththththththt" There is a lot of airflow, so I don't think there is anything wrong with the fan itself. I removed the glovebox, and can see the valves open and close when I move the selector ****.

The sound is the loudest (and its really loud) when I have it on any setting other than defrost, although I can still hear it. And of course it's the loudest when the fan is on high, and gets almost unnoticeable at about low-mid setting.

I dont think i can see anything without taking the entire fan assembly out. :/

 

I think you'll have to take the fan assy out. Sounds like something is rubbing against it or fluff/dirt built up on the fan putting it off balance, maybe even the bearing is on it's way out.

 

lol could it be a leaf? that happens to mine every now and again, they like to suck in leafs the way the opening is designed.

 

it might be a leaf, it is parked under a tree. where is the outside intake located?

 

im not exactly sure, If i had to guess i would say that plastic piece that goes across the bottom of your windshield. that's probably the only place they could get sucked into i think, and when you have your air on high you can hear it sucking in air. There's a plastic piece with the grates then theres the piece above that with a small gap between it and the windshield that is perfect for a leaf to fit into, and i think that's where they get sucked into. the other day mine sucked one in and it was making a horrible noise, and i just kept playing with the fan speed and it finally stopped. anymore i clear the leaves off before i start my truck.

Edit: dont know what i was thinking. those two plastic pieces i was mentioning are one piece. but what step66 said is what i would do.

 

The cowl vent lets in all sorts of leaves this time of year:normal! Its been happening since they put heat in cars. Run it for a couple weeks until fall ends in the Seattle area and if it doesn't go away by mid Dec just throw a new blower motor in! 'cause if it IS the motor,it will get worse when colder temps come and you will want full ventilation for the winter!