Repetetive HVAC Popping Noise at Morning Start
09-27-2012, 05:36 PM
#1
Repetetive HVAC Popping Noise at Morning Start
Sorry in advance for the length of this, but I'm getting frustrated with this issue and want to get all the details out.
A while ago, I had the first HVAC issue since buying my 06 A6 a couple of years and over 60k miles ago. It was the issue where some vents would actually blow hot despite the A/C being on. That was repaired per the TSB. A little while after that I started experiencing the issue below. It could be totally unrelated, but I wanted to give the history and I am fairly confident I never heard it before this repair.
In the mornings after sitting overnight in my garage, there is a popping noise that sounds like it is coming from under the dashboard. It is repetitive and occurs roughly every 4 seconds. It sometimes can be heard alternating from the driver's side to the passenger side. It stops when the HVAC is turned off, but comes back when it is turned on. It goes away after the car warms up. It almost never occurs again at any other point in the day even after the car sits for many hours when I'm at work. I have noticed it reoccur once (still early in the drive) and once it didn't start until 5 minutes or so into the drive, but those are the exceptions.
I was able to capture the noise and created a video noting the noise to distinguish it from other in-care noises: http://youtu.be/bmEafWaEKL0
By some trial and error I was able to figure out that it is related to the heat and stops if only the A/C is on.
I brought it in to a dealer and replicated the noise for the tech. They replaced 2 HVAC flap motors they stated were making noise. That didn't fix the issue. I brought it back in and their most recent attempt at making adjustments does not seem to have fixed it. It was actually indicated to me that this may be normal, but I challenge that and am still not entirely sure they heard the same noise since I did not replicate it this time. I did just noticed they apparently found a sporadic fault (1 time) for comfort bus in single wire mode. Might not be related, but it was something that was noted.
The morning-only aspect is one of the more perplexing things for me. As a theory, perhaps the car only does it in the morning because it gets to sit overnight in the cooler temperatures vs. sitting in a parking lot in the summer/spring/fall warmth. This only started in late spring so it has not sat in a parking lot with low all-day temps.
Does anyone have any idea of what could be causing this and a fix?
A while ago, I had the first HVAC issue since buying my 06 A6 a couple of years and over 60k miles ago. It was the issue where some vents would actually blow hot despite the A/C being on. That was repaired per the TSB. A little while after that I started experiencing the issue below. It could be totally unrelated, but I wanted to give the history and I am fairly confident I never heard it before this repair.
In the mornings after sitting overnight in my garage, there is a popping noise that sounds like it is coming from under the dashboard. It is repetitive and occurs roughly every 4 seconds. It sometimes can be heard alternating from the driver's side to the passenger side. It stops when the HVAC is turned off, but comes back when it is turned on. It goes away after the car warms up. It almost never occurs again at any other point in the day even after the car sits for many hours when I'm at work. I have noticed it reoccur once (still early in the drive) and once it didn't start until 5 minutes or so into the drive, but those are the exceptions.
I was able to capture the noise and created a video noting the noise to distinguish it from other in-care noises: http://youtu.be/bmEafWaEKL0
By some trial and error I was able to figure out that it is related to the heat and stops if only the A/C is on.
I brought it in to a dealer and replicated the noise for the tech. They replaced 2 HVAC flap motors they stated were making noise. That didn't fix the issue. I brought it back in and their most recent attempt at making adjustments does not seem to have fixed it. It was actually indicated to me that this may be normal, but I challenge that and am still not entirely sure they heard the same noise since I did not replicate it this time. I did just noticed they apparently found a sporadic fault (1 time) for comfort bus in single wire mode. Might not be related, but it was something that was noted.
The morning-only aspect is one of the more perplexing things for me. As a theory, perhaps the car only does it in the morning because it gets to sit overnight in the cooler temperatures vs. sitting in a parking lot in the summer/spring/fall warmth. This only started in late spring so it has not sat in a parking lot with low all-day temps.
Does anyone have any idea of what could be causing this and a fix?
09-28-2012, 04:26 AM
#2
I'm going to guess the blend flaps were not setup correctly. i'm thinking that the blend motor is trying to move the flap to a position where it cant go and the plastic gears are jumping causing the pop sound, I think it gives up after so attempts and should store it as a fault. Check with a Vag Com to see if there are any faults. If you dont have a Vag Com try turning on the heat up at night before you park the car and see what happens the next morning.
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