Humming noise from behind the dash when A/C is on or when temperature is below 5 celcius

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genetixx01
Posts: 8
Joined: Sun Aug 08, 2021 6:49 pm
Location: Montreal

Humming noise from behind the dash when A/C is on or when temperature is below 5 celcius

Post by genetixx01 »

Hi genvibe community. I have been using this forum for years now but it's the first time I write a post. I used to find all information I needed from the current posts, but for my current problem, my researches so far haven't been successful, so I decided it was time for me to create a new post. Actually, I found this very long topic https://forums.genvibe.com/phpBB3/viewtopic.php?t=10269 that could be useful, but its last reply is from 2006, so I decided to start this new one.

I'm the owner of a 2005 Pontiac Vibe base model. Here is my problem. For a few years now, I have been hearing what I would describe as a humming noise coming from the ventilation when either the A/C is on during summer or when it's below 5 degrees Celsius outside (fall and winter) and the heater is working. The noise is mostly hearable when the car is on idle, but remain then when the car is moving, although the road noise is masking it at a certain speed. Even in the conditions mentioned, the noise is not there 100% of the time, but I would say most of the time. During summer, if I turn the A/C off but keep the fan, the noise stops. During winter, to stop the noise, I need to turn the fan off.

This video https://www.youtube.com/watch?v=yrGuT_rjf68 gives a good idea of the sound I'm hearing from inside the car through the ventilation. I kind of humming that seems to be a bit related to the engine RPM.

Here is what I did to try to target or resolve the problem :
- I disassembled the blower behind the glove box, and it wasn't damaged or dirty at all and nothing changed when I reassembled it.
- I replaced the water pump (that was anyway leaking) and it hasn't solved anything either.

Reading from multiple posts and looking at multiple YouTube videos, it now seems that the problem might be related to the AC compressor. However, this would not explain why I'm hearing it when it's below 5 degree Celsius, since only the heater is working at this temperature. And the noise actually appeared during winter before I heard it more recently with the A/C. But lets' assume it's the A/C compressor, I'm then wondering if I can resolve the problem just by replacing the compressor clutch or if I'll need to have the compressor replaced.

In the long topic I linked above, the guys had to replace the A/C compressor twice ad then even that the noise cam back again after 6 months, so I'm a bit afraid to invest in a new compressor considering the car is old. Plus, I can't hear its noise, so I can't be sure it's the same. I have to mention that the A/C is still working, but I think it's a bit less cold that it used to be. But it just takes a bit longer to cool the car when it's very hot, and it's not a problem to me. What's bugging me is the noise.

If one of you have any experience with this kind of problem, please feel free to share your knowledge! Thank you very much in advance!
Trying to stretch the life of my 2005 Pontiac Vibe
andrewclaus
Posts: 482
Joined: Tue Oct 03, 2017 6:38 pm
Location: Golden, CO

Re: Humming noise from behind the dash when A/C is on or when temperature is below 5 celcius

Post by andrewclaus »

My most recent experience was a leaf in the blower motor and you already checked that.

First I would try to pinpoint the source of the noise with a mechanic's stethoscope.

You do know that the A/C comes on for defrost mode in winter, right? In this car, it's for both modes that put air on the windshield, defrost and defrost/panel.
genetixx01
Posts: 8
Joined: Sun Aug 08, 2021 6:49 pm
Location: Montreal

Re: Humming noise from behind the dash when A/C is on or when temperature is below 5 celcius

Post by genetixx01 »

Hi andrewclaus,
Thanks for your reply! Sorry for the late reply, I'll have to review my setting because I haven't received any email notification...

First, I thank you to let me know that the A/C will start on defrost mode, I didn't know that. This means that it's pretty sure it's the compressor. I only hear this sound when A/C is on during summer or when I defrost during winter. So I think you pinpointed the problem already.

Now, I'm wondering how I can know if the whole compressor is broken or if I can solve this problem by only replacing the compressor clutch. Any idea how I can guess that?

Many thanks!
Trying to stretch the life of my 2005 Pontiac Vibe
andrewclaus
Posts: 482
Joined: Tue Oct 03, 2017 6:38 pm
Location: Golden, CO

Re: Humming noise from behind the dash when A/C is on or when temperature is below 5 celcius

Post by andrewclaus »

Glad that helps a little, but that's as far as I can go. I've never had to, or wanted to work on a compressor. Good luck with it.

The weather where we live is temperate and arid enough that it's optional, so if it breaks that far I'll just let it go. Our house doesn't have A/C. And we're old enough to have grown up without A/C, in a humid Midwest state, so we just nut it up and turn on a fan.
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joatmon
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Location: SMC MD

Re: Humming noise from behind the dash when A/C is on or when temperature is below 5 celcius

Post by joatmon »

Seems unlikely that it would be the compressor clutch. The clutch itself never moves, it just generates a magnetic force that pulls the end late in so it grabs the spinning pulley. Similarly, there's a bearing for the pulley, but if it were bad, I'd expect it to make a noise when the AC was not running. When its running, the pulley, compressor, and bearing are all spinning together with no slippage.

If its been this way for a few years, and seems to be working OK, then I'd probably just try to ignore it unless it gets radically worse or fails
andrewclaus wrote: Sun Aug 15, 2021 4:18 am ... we're old enough to have grown up without A/C, in a humid Midwest state ...
I'm old enough to have grown up without AC in a humid coastal atlantic state, and I'm in one now, and I'm addicted to AC. to digress, how bad's the wildfire smoke out there in Golden? I was out near there several times this summer, some days it was pretty bad.
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andrewclaus
Posts: 482
Joined: Tue Oct 03, 2017 6:38 pm
Location: Golden, CO

Re: Humming noise from behind the dash when A/C is on or when temperature is below 5 celcius

Post by andrewclaus »

joatmon wrote: Sun Aug 15, 2021 11:38 am...to digress, how bad's the wildfire smoke out there in Golden? I was out near there several times this summer, some days it was pretty bad.
The smoke from CA and OR got pretty bad the last two weeks. It's better this week, but there's more coming in.

Your tips on the compressor operation make sense. Maybe one of these days I'll work on one.
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