I have an 03 Accord that just turned to 67k miles. It just started making this weird noise last night. Since it was chilly out last night, I had my heater turned on and the vent control set to feet and windshield defrost. When accelerating or at a stand still and I rev up the car, it makes this weird humming noise and grows louder as the car gets higher in the RPM. The weird thing is, if I press on the gas and it makes the noise and I switch the setting to face, the noise goes away instantly. Anyone know what it could be?

 

I just went on my lunch break and tried to play around with the AC\heater settings. It appears to be the AC compressor? The thing I don't understand is the the A\C is set to off but the noise only occurs on the defrost settings. Does the A\C compressor come on when defrost is selected and the A\C light is off? The just seems weird to me because when I select defrost, i hear the compressor kick in but there is no light next to the A\C button. Also I then selected the face blower and then turned on the A\C and same noise. When I turn off the A\C and leave on the face blower, no noise. I probably should add that last summer my A\C didn't work very well as in getting cold but did work a little. Any ideas why the compressor would kick on while set to defrost?

 

The a/c will act as a dehumidifier and remove moisture from the air.

My 5th gen accord does not use the a/c to defrost. I didn't realize that yours does.

 

Used to own a 1998, and when you select Defrost, it would switch ON the AC & the green lamp would light up for AC. And you could then switch it off.

But my 2003 acts the same way as yours. With the 2003, the AC runs but the green lamp is not lit. And you can't switch it off.

 

I just figured how to switch it off. with your car off and your fan setting off, Hold down the A/C and recirculation button. While holding down these 2 buttons, start the car. Keep holding both buttons down. The recirc button will blink a few times, keep holding the 2 buttons in. The A/C button will light up. Let go of the 2 buttons. Now it will act like your 98 accord.

Does anyone know why my car would make that noise when the A/C compressor is on. Low on freon? or something else?

 

You could check freon but more then likely sounds like possible bearings start to go bad or gone in the ac compressor or the clutch. Considering you only hear the noise when compressor is on I would say the compressor itself is the culprit.

 

My V6 EX Ciupe started making this noise too when the defrost heater was on and when rpm went over 2000. I had recently changed the V- belt to a Good year brand but just changed it again to an OEM Honda belt. No more noise. I think the noise was from the vbelt when the alternator was powering too much and the belt was maybe a bit loose being an aftermarket one.