radjaco

Hi, everyone. I have 1997 A8 3.7 FWD.
I noticed that when I start the car some sound as if a heater sound comes on (like you blow into an empty tank); then I press 'on' button on the dash AC and the sound goes off. After I have to press 'off' button to turn off the AC. I do not have AC charged with gas.
If anyone knows what this is I would appreciate.

jfrahm

On USA cars, (at least facelift cars) the A.I.R. blower runs briefly after startup to inject air into the exhaust and get the cats up to operating temperature. This would not be affected by the AC switch.

radjaco

Thanks for explaining. I understand but what I have to do? Keep it running and wait until it goes off? It is little annoy7ing but I can wait if it goes off itself. Will it? However, what worries me is that when I turn the AC on and then off the sound stops and it seems it turns off too. Thanks again.

silverd2

Yep, on USA models, the SAI (secondary air injection) should run the first 90 secs on cold start-ups. It's an after-burner for overly rich start up mixture ... oxygen after the exhaust valves to ignite and finish burning unburnt fuel mixture ... and heats up the cats, which only work correctly when very hot.

If the noise is really noticeable, the air pump may have a bearing going bad ... common problem. The replacement bearings are exactly the same as those used in skateboards and longboards ... dirt cheap... just rebuilt the pump for my Allroad for about $1.25, with the best bearings I could find.

radjaco

Thanks, so you mean the blower motor bearing? So take out the blower motor and replace the bearing. Is this the procedure audipages Fresh Air Blower Replacement
?
Or there is another motor bearing you are talking about?

radjaco

Where is the air pump? Could you please post the procedure if I am wrong with the link above.

silverd2

I used this as a guide >>

quattroworld.com Forums: Behind and below the junction of the y-pipe...

In A8's the pump is in the bottom of the air cleaner box.

radjaco

Thanks. Is this the location as in a picture?

radjaco

Just by any chance, do you have the bearing size or number to get in a shop?

jfrahm

It's in the rebuild thread, 608's.