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How to Bleed Air from Heater Core

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Old 03-11-2014, 02:53 PM   #1
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Default How to Bleed Air from Heater Core

I just replaced the water pump on my 99 A8. Before the pump went out, the heating system worked fine inside the car and the temperature of the air couming out of the vents was perfect to whatever I had it set to. After filling the coolant, I started the car and attempted to bleed the air out of the system. I've done this a couple of times but still no warm air out of the vents. I have to assume I don't have the correct procedure down for bleeding the air. Can anyone provide me with instructions on how to do this? At first, it seemed simple enough, but after striking out twice, I'm puzzled as to what I'm missing. Thanks in advance!
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Old 03-12-2014, 07:01 PM   #2
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I'm not sure about the PFL but the FL cars have two bleeder valves on the lines going through the firewall.
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Old 03-21-2014, 06:26 AM   #3
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Originally Posted by ggjoy View Post
I just replaced the water pump on my 99 A8. Before the pump went out, the heating system worked fine inside the car and the temperature of the air couming out of the vents was perfect to whatever I had it set to. After filling the coolant, I started the car and attempted to bleed the air out of the system. I've done this a couple of times but still no warm air out of the vents. I have to assume I don't have the correct procedure down for bleeding the air. Can anyone provide me with instructions on how to do this? At first, it seemed simple enough, but after striking out twice, I'm puzzled as to what I'm missing. Thanks in advance!
You've probably already worked this out by now, but I only use the bleeder screws (or hose holes on other cars) as a starting point...fill to overflow, tighten down, then:

I go the old fashioned route (still recommended by Bentley) of starting the car with heater set to HI and running the car (sitting still) at 2000-2500 rpms for 5 minutes plus, reving to over 4000 rpms several times during this. During this time, I'll hear a quiet "pop", fluid flow, then a giant blast of heat. I top off the reservoir to "max"...then maybe a couple days later, top it again if needed.

After this, I have never had lingering air in the system with any car, including my D2.

Job done.

Last edited by silverd2; 03-21-2014 at 06:30 AM.
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