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Discussion Starter · #1 ·
Hi All,

So, my AC works sometimes (2004 V8). I can get in the car and it will blow warm. Run into the store, start it back up and it will be ice cold. Sometimes it will be blowing nice and cool and then decide it would much prefer to blow warm air. No rhyme or reason to it.

I did evac and recharge the system but that did not help. I would think that if it was the compressor that it would either work, work poorly, or not work at all.

Seems like it could be some sort of actuator or sensor or flap that is not moving. No idea where to even begin looking so any expertise or experience is welcome.

Thanks.

Mike
 

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Discussion Starter · #3 ·
Hard to tell if compressor is running when warm, I guess I can hook up to Vag and find out. Engine fan does run.

It does seem like the compressor switches off and then does not always come back on. Yesterday morning I had no AC during a 30 mile trip. I even tried turning car on and off to know avail. On my return trip, after car was parked for 30 minutes, I had ice cold AC for about 20 minutes, then I could feel the air suddenly turn warmer and damp as if compressor was no longer engaged. It stayed that way for 20 minutes. After car was again parked for a few hours, 90 degrees outside, I started it and had ice cold air for the next 40 minutes until I arrived home.

Thus, I am theorizing that it is something electrical. If it were compressor, low freon, etc. I would expect it to act consistently. It seems more of an on-off type situation.

I did replace cabin filter and system was evacuated and refilled with proper refrigerant gauges and scale.

Thx.
 

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Without a VCDS scan we are guessing.
 

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VCDS would allow you to monitor the hvac control module 008 measuring blocks for compressor activity, system pressures, etc.
 

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I had a similar experience and I think it has to do with the automatic mode adjusting the temp in relationship to the outside temp. It really only does it in early spring or late fall when the outside temps aren't extreme. For instance, if the outside air is showing 68 and I want to run the A/C at 72 because the interior heated up from the sun, it'll try to turn the heater on so that the ambient air it's blowing in is at 72.


When it does this, I first punch the button to control both front A/C's from the same switch and set it a little lower than outside temp (read the outside temp on the dash display). Then I punch the button to control both rear A/C controls and do the same. Then you can adjust to suit once the auto mode is off. It's just a matter of out thinking the computer.


As soon as the temps here get to where the low doesn't fall below 80 it'll work fine all the time.


Perhaps there's a VCDS setting to put the A/C into manual all the time.
 

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Discussion Starter · #8 ·
I had a similar experience and I think it has to do with the automatic mode adjusting the temp in relationship to the outside temp. It really only does it in early spring or late fall when the outside temps aren't extreme. For instance, if the outside air is showing 68 and I want to run the A/C at 72 because the interior heated up from the sun, it'll try to turn the heater on so that the ambient air it's blowing in is at 72.


When it does this, I first punch the button to control both front A/C's from the same switch and set it a little lower than outside temp (read the outside temp on the dash display). Then I punch the button to control both rear A/C controls and do the same. Then you can adjust to suit once the auto mode is off. It's just a matter of out thinking the computer.


As soon as the temps here get to where the low doesn't fall below 80 it'll work fine all the time.


Perhaps there's a VCDS setting to put the A/C into manual all the time.
I have considered that it is some sort of temp sensor. However, even on a hot day if I drop it to LOW or low 60's it still does not seem to trigger the compressor on (or blend doors off, or whatever is amok).

Given that the problem comes and goes makes it even more challenging. I could take it to the stealer only to have it work perfectly while there and then stop on the way home.

Thanks
 

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Discussion Starter · #9 ·
So, I ran a log file and discovered the following. Sounds like it is a bad interior temp sensor (I think that is the one near the interior air filter)? Would you agree?

Address 08: Auto HVAC (7L6 907 040 H)

17:57:23 Group 012: Temperature
25.0°C Left Body Outlet Temp. (G385)
24.0°C Right Body Outlet Temp. (G386)
26.0°C Left Footwell Vent Temp. (G261)
23.0°C Right Footwell Vent Temp. (G262)

17:57:23 Group 013: Compressor && Shut-Off Criteria
8.0 Compressor Shut-Off
- Compressor Current
- Compressor Control
874 /min Compressor Speed

17:57:23 Group 011: Temperature
30.0°C Outside Air (G17) Temperature
29.0°C Interior Temp. Sensor
1.0°C Fresh Air (G89) Intake Duct
90.0°C Coolant Temperature
Reply, Reply All or Forward | Mo
 

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Discussion Starter · #10 ·
Yes, indeed it was the temp sensor. All fixed! Part number 1K0907543G

It is located near the blower motor, closer to the middle of vehicle. Remove the panel with the interior light, shine a flashlight and you should see it. The part twists to remove then unplug wire harness. Installed new part and good to go, no more crazy temp readings via VagCom that were shutting down compressor.
 

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Yes, indeed it was the temp sensor. All fixed! Part number 1K0907543G

It is located near the blower motor, closer to the middle of vehicle. Remove the panel with the interior light, shine a flashlight and you should see it. The part twists to remove then unplug wire harness. Installed new part and good to go, no more crazy temp readings via VagCom that were shutting down compressor.
Can you give a better description (or photo) of where this part is? Mine had the same symptoms (as I described earlier) and so I got a new part to put in. I removed the panel under the dashboard in the driver's foot well with the little light on it. I looked all around - up behind the gas and brake pedals and towards the center console - and didn't see the part. Is it under the passengers side? I couldn't even see how to get the passenger foot well panel loose.
 

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Discussion Starter · #14 ·
Yes, that is the part.

Did you do a VagCom analysis? That is easiest way to see if / when compressor is shutting down and why. Otherwise, you risk just randomly throwing parts at it until you find the problem.
 

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Yep - that's it. It took about 5 minutes once I knew where the part was.


I've run a VagCom scan but I didn't do the individual sensor readings like you did on yours. Mine was acting up just occasionally, but when it has a mind to it'll blow VERY COLD!! Then when the 107 degree temps hit the other day with internal car temps much higher it decided that it didn't want to work at all. I'd drive for about 15 minutes blowing ambient temp air while playing with the knobs, then suddenly it would decide to work and blow VERY COLD.


Fixed it today, but we're having unseasonably cool temps in the mid 70's so it's hard to tell if it'll work right. I'm heading out to go get dog food and I'll have a chance to try it.


Thanks to all for the ideas on the fix, the part number, and the diagram!! Y'all are great!!!
 

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And that fixed it. Headed to the dog store and it blew cold right away.


In the meantime I've ordered a new cabin filter so I'll leave the panel off until I get that changed, too.
 

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Yes, indeed it was the temp sensor. All fixed! Part number 1K0907543G

It is located near the blower motor, closer to the middle of vehicle. Remove the panel with the interior light, shine a flashlight and you should see it. The part twists to remove then unplug wire harness. Installed new part and good to go, no more crazy temp readings via VagCom that were shutting down compressor.


Good feedback, thanks.
 

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My 2004 V8 is doing this, and I knew if I searched the forums I would find the solution. Thanks for posting guys!!
 

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Thanks to this thread, I have just fixed my 2003 v6 air con that decided it was not going to work.

I was just going to have it re gassed, glad I read this first. I checked with Vcds and the temperature sensor was showing -25 C when the ambient temperature was 20 C.

The AC is now colder than it has ever been.
 

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Hmmm, my AC suddenly stopped working, the tech said the pump was gone but it happened suddenly.

Worth looking at before I spring for a compressor and go through all that to fit it.
 
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