I have a 2002 Honda Accord coupe with 130K miles on it. A few days ago the AC started to make a loud roaring noise when it is turned on full blast. As you turn it down the noise gets quieter and when the fan is on low the roaring noise stops. Other than making this sound it is running fine and there are no other issues/noises coming from the car. Anybody know what is causing this noise?
Sometimes, the foam-type material that is used between sections of the HVAC ducting becomes partially dislodged as it dries out, and can cause strange noises when the fan is on the higher speeds. It is also possible that there is something (like a leaf or a twig) caught in the squirrel-cage blower.
If the problem is some partially dislodged foam, you will soon see some strange particles flying out of the dash vents when it becomes completely dislodged. At that point, the noise will likely disappear. And, a leaf or a twig in the blower will eventually get worn down to the point where it no longer makes noise. These are the two most likely situations.
But…have you tried running the HVAC fan on just the “vent” (non-cooled air) position to verify that the noise actually has nothing to do with the A/C itself? If not, I suggest that you do so.
You have leaves and/or other types of debris, like twigs, in your blower motor (also known as a squirrel cage). A mechanic who knows how to take it apart should be able clean it out in about 15-20 minutes. The only tricky thing that might make it take longer to clean out is the blower motor’s proximity to the passenger airbag, so for that reason, I leave this type of thing to a professional.
With the fan on high, switch from outside air to inside (recirculation) air and see if the roaring part goes away. If so, it means that one of the inlets is blocked. If not, something is in the squirrel cage. Its an easy job. just three screws and one connector, located behind the glove box, next to the kick panel and drops straight down.