1999 Suburban AC Noise

I have a 1999 'Burb K2500 with 105K miles on it. We had a heat wave (for us) last week.
When my wife ran the AC on the "Max" setting, there seemed to be a thumping
sound coming from the passenger's side of the vehicle. I was able to duplicate it when I was driving.
It runs fine on the regular AC setting.
I'm going to take it to my mechanic to have him check it out tomorrow. I don't mind not using the "Max" setting--but I just want to make sure the whole AC system doesn't die on me some day.
Any ideas what might be going on?
Mark "Those who live by the sword get shot by those who don't"
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On 28 Jun 2006 11:19:28 -0700, Mark Filice

The Max setting changes the airflow from outside the car to recirculate. Likely what is happening is that the door that selects between outside and inside is hitting something or the mechanism that moves the door is malfunctioning. I honestly don't know what they used, on this late model, to move the door (vacuum, electric servo, gerbils?). This door was, on my 89 S-10, on the passenger side.
You can test for this by moving the temperature selector away from "Max" and then pressing the "Recirculate" button (at least, I could do this on my 98 Suburban. This is assuming that you have the knobs and buttons setup, like I do). This moves the air door.
Any funky hissing noises in the cabin or under the hood? (while the car is running. If you get hissing while the car is off, be careful! It could be a snake, or worse, an angry cat!)
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I know there is a air filter someplace in the system, perhaps it is plugged with dirt, so when you go to Max the air flow rate changes and causes the filter to suck in and out??
Mark Filice wrote:

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snipped-for-privacy@hotmail.com says...

about it. On the way there, I tried to duplicate the problem and of course it wouldn't do it for me.
But I did notice that the air flow seemed to fluctuate instead of remaining at a constant flow. The mechanic is going to look at it--he told me there might be a door that closes over the outside air flow that might be making the noise. A filter problem could also be the culprit.
I mentioned the air flow fluctuation to him and he will check it out.
I've been bringing my vehicles to him for over 10+ years and he is always been great to me--so he'll most likely figure it out.
Thanks!
Mark "Those who live by the sword get shot by those who don't"
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On 29 Jun 2006 11:39:29 -0700, Mark Filice

Another .02
My 98 model does not have a cabin air filter (or so I am told). Hey, if they find one in yours, let us know where it is, so I can check mine. Other people have been wrong before.
Your mechanic mentioned the door that closes to shut off outside air flow? He's a GENIUS! :-)
Jeff
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snipped-for-privacy@hotmail.com says...

carpeting on the passenger side had come unglued. It was being sucked in and out of the cover over the air intake.
The mechanic cut the matting away from that area and the problem was solved. I stopped by to pay him today--and he said he would add it on to my bill the next time I brought it in.
I've heard this story before with a couple of other minor things I brought my vehicle for in the past. The real translation is that he isn't going to charge me at all.
That is why he has been my mechanic for 10+ years.
Mark "I love cats. I just can't eat a whole one by myself."
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