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Old 12-02-2008, 08:14 AM   #1
MudWalker OP
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02 Audi A4 - Got No Heat

It's been in the shop for a week now and the service manager told me yesterday he is stumped. The car makes a little heat when under power but looses all heat at idle. Temp. gage normal, warm-up normal, climet control system seems normal. WTF??????? How come a Porsche, Audi, VW dealer can't figure this out??????

Did all the stuff.....
Water pump
Flush heater core and got some gunk out
System flush and bleed
Back flush cooling system

Should I take the car back and try myself, don't want to sell, it's paid for and in great shape and we like it.

Any ideas out there??????????
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Old 12-02-2008, 08:26 AM   #2
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Thermostat stuck in open position?

Does the car come up to temp on the temp gauge?

Plugged heater core?

Bad cabin temp sensor?
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Old 12-02-2008, 08:49 AM   #3
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Do you have, can you borrow an IR temp tool and scan the heater core to prove heat or no heat at the core? You could also do this to the feed and return lines under hood going to and from the heater core. This will prove/disprove the flow of hot coolant. Vacuum problems? causing vent doors to open/close at the wrong times? All elec heater control?

Not related, but you did use G11 or G12 coolant?

Replace the thermostat if you have not done so cheap and easy unless this is the one that is buried down by the pump?

If you mechanic is an IATN (International Automotive Technician Network)member...
Have him post the problem with all he has done and the world will come to the rescue.

May need more info.
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Old 12-02-2008, 09:29 AM   #4
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Are you talking about the air temperature coming out of the vents or the engine coolant temperature. If it is making hot coolant (grab onto the small coolant hoses coming from the motor to the heater core) then the problem is with the heater core, the shutoff or bypass valve(allows flow through the heater core or shuts it off or shunts it) or the mixer door.
The shutoff valve on newer vehicles is usually vacuum controlled(or sometimes solenoid or electric motor), probably from the climate control module. My money is that something is going wrong with it or the part that controls it causing a reduction of flow to the heater core.
Next bet is the cold air mix door not shutting fully. In the airbox the door will open to allow some cold air to mix when it is not fully at the hot setting. Usually these doors have foam rubber seals and sometimes they tear and get stuck in the mechanisms or just leak enough to cause problems. The door is probably controlled by vacuum motor, again from a signal from the climate control. You might be able to see the door armatures etc from the passenger side of the car behind the centre console or by pulling apart the glovebox.
I don't have any experience working on Audi's but all cars and trucks use similiar systems, just the mechanism of implementation changes. Hope this helps.
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Old 12-02-2008, 10:39 AM   #5
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Thanks for the info...............

- T-stat new, buried by oil cooler, expensive replacement.
- engine warms up to normal temp in normal amount of time.
- Heater core did spew out some gunk but is running clear with water flush.
- Temp sensor could be bad but computer diagnostics should pick up fault.
- Heat is going to core, hoses are hot but with apparent low flow rate.
- All heater/AC controls are electric not vacume acuated.
- Always dealer serviced, always factory fluids.
- Dealer has contacted their Audi Guru.
- Air temp at vents in car is just warm and drops off to cold at idle.
- 100% coolant flow to core 100% of time, no bypass valve.
- Cold air supply not issue because system has recirculation mode and when activated same result.
- Audi onboard computer diagnostics will monitor all climate control systems so any system fault should get picked up. Yea right!

Sorry guy's, keep em coming.
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Old 12-02-2008, 12:52 PM   #6
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Hmmm... sounds like a faulty flap positioning motor. Yes, every flap in that car is opened/closed by motors/actuators, not cables. If the flap was stuck closed air would still blow out the vents, but it would be cold as hot air is not being mixed in.

HVAC codes are logged by VAGCOM. You'll need to read the codes with a VAGCOM tool, OBD II will not read the extended VAGCOM codes. The VAGCOM software & cable are pricey, like over $100 bucks. But the internet is full of Audi owners who share their VAGCOM tools.

Could also be the HVAC head unit, but my guess is a flap positioning motor. But start by getting a VAGCOM diagnostic.
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Old 12-02-2008, 01:20 PM   #7
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Quote:
Originally Posted by MrBadExample
Hmmm... sounds like a faulty flap positioning motor. Yes, every flap in that car is opened/closed by motors/actuators, not cables. If the flap was stuck closed air would still blow out the vents, but it would be cold as hot air is not being mixed in.

HVAC codes are logged by VAGCOM. You'll need to read the codes with a VAGCOM tool, OBD II will not read the extended VAGCOM codes. The VAGCOM software & cable are pricey, like over $100 bucks. But the internet is full of Audi owners who share their VAGCOM tools.

Could also be the HVAC head unit, but my guess is a flap positioning motor. But start by getting a VAGCOM diagnostic.
Sorry new ground here, what is the head unit.

I'm not a mechanic, I'm just trying to learn so if tomorrow they still don't have an answer I can say "yea but did you check the flap positioning motor?" I did find refrence to this when google searching yesterday and I think you may be on the right track with this.

But the car is being fixed by the dealer, would they not check this with factory diagnostic tools? Is scanning the computer not SOP.

I have to say, so far I am being treated well, The car has been with them for over a week after their first attempt which included flush and system check (among other things I needed anyway). As the problem returned the next day I brought it back they have again provided a sweet 08 A4 for me to drive and so far have only billed me 2 hours labor as they search for the fix. I've also posted on some Audi sites but so far got much more response here in the garage.

Thanks again, anything you can think of I should ask the service manager to check?
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Old 12-02-2008, 01:50 PM   #8
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I bet it is the thermostat.
On this car it's not a thermostat at all, it's actually another temp sensor.
This device actually senses temperature and then signals yet another valve type device to open or close the flow of coolant. This isn't better than the old way, I reckon.

My 2 cents

Stu

CA Stu screwed with this post 12-04-2008 at 03:27 PM
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Old 12-02-2008, 02:01 PM   #9
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Thanks Stu, I'll be talking about this flap with them tomorrow. This makes most sence to me.

Blend flap allows fresh air to mix with heated air? If so, why no heat when recirc. is selected? Unless this flap is the recirc. and is stuck wide open.......

Why do they have to make this stuff so complicated???????
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Old 12-02-2008, 04:38 PM   #10
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Went into my e-bahn reader.....
Factory type VW/Audi manual to help but I have not installed the Audo stuff Only My VW stuff.
But, since the dealer is working on it they have all of this and more so?????
The bland door is sort of the recirc. door on most cars. As far as elec. controls go, if a temp sensor in the HVAC system was reading wrong the computer and diagnostics may never catch it. It has to fail for a flag to be thrown in most cases. Sound a bit like a flow problem. Could be air in the system. I assume they ruled this out. Can't be this easy, but, has the cabin air filter been changed? And, sometimes even if it has been changed some particlate (stuff) can fall into the ducts and jamb up ?????.

Just thinking out load
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Old 12-02-2008, 05:51 PM   #11
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Quote:
Heater core did spew out some gunk but is running clear with water flush.
-
I replaced a heater core last month for the same problem.Customer compliant was "no Heat".Both hoses were hot and flowing,but when the heater box was opened enough reveal the core,the IR temp gun showed only part of the core was flowing hot water,the rest of it was blocked.Not enough heat surface area for the amount of air flowing over it.
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Old 12-02-2008, 06:23 PM   #12
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Quote:
Originally Posted by MudWalker
- Heat is going to core, hoses are hot but with apparent low flow rate.

Sorry guy's, keep em coming.
Have they checked to make sure the cooling system is pressurizing properly?

Cracked radiator, bad radiator cap, bad water pump could result in low coolant pressure which could equal low/no flow to the heater core.
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Old 12-02-2008, 07:08 PM   #13
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Don't know that press would affect flow.

Boiling temp yes!

The IR temp gauge to all parts of the core sounds like a real good idea.

Er, I like it
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Old 12-03-2008, 05:58 AM   #14
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I too have been thinking the bottom of the core could be completely gummed up and just the top portion of the core is taking coolant. I would attempt to check the volume of liquid going in to the existing isolated heater core compared to a new core. Just fill the inlet hose until water comes out the outlet and keeping track of how much water went in. Then repeat with a core on a bench with the same hoses on it.

They tell me it's a 12 hour job to replace the heater core and the get $60/hr. What about chemical cleaning the core with something to break up the gunk?????????????
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Old 12-03-2008, 07:41 AM   #15
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You might try running some radiator flush thru the system.


Mitchell on Demand only shows 3.9 hrs to replace the heater core on an a 02 A4 Audi,I always add an extra hour to cover the little odds and ends that crop up....but 12 hours...maybe you need to check with some one else..
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