ripping my hair out on this one off issue please help

[Cizx]

So I have a 2007 GTI and I've had the issue where my car will overheat with the AC on. When I idle the air starts to heat up and get extremely stale. Here is what I've done so far and whats happened. I've replaced the Cooling fans, when i plugged them in the small one spun instantly then shut off. I've replaced the fuses, temp sensor, and the temp sensor pigtail. Small fan has been the issue it never comes on with either fan assemblies and of course causing the big fan to overwork it's self.

[mjmallia]

Plug into VCDS if you have it or know someone local to you, to get the error codes.

Is the econ light on permanently, even with press the the button?

[Cizx]

So no Econ light and no codes what so ever old get a code when the car over heats for the over heating

[LC5F]

There are 2 temperature sensors - one at the side above the bellhousing and another on the front in the thermostat housing  - have you replaced both?

[Cizx]

No I have not. I did not know that now is it the same sensor or is there a different part number

[LC5F]

Seem to recall they are the same part - but please check.
I am guessing it's the one at the front you have not done, it is not the easiest to get at, alternator off and under the intake manifold - I appreciate you have thrown a lot of money at this, but consider replacing the thermostat at the same time

[Cizx]

Sounds like a good idea I’d rather not have to tear into this again I like to take the long way to ensure proper repair if that makes sense

[pudding]

I could be wrong, but I believe the front temp sensor is for fuelling compensations, being in the water pump output flow, and the gearbox side one is for triggering the fans/dash temp gauge as it's the output from the radiator.

Is your car a DSG?  I believe they have an extra thermostat in the temp sensor housing, above the gearbox housing where LC5F mentioned.  Could this be stuck shut perhaps?  Manuals only have the main stat at the front.

[Cizx]

It is I didn’t know that could that be an issue?

[pudding]

In that case, I would personally replace that whole thermostat/temp sensor assembly.  If the secondary stat is jammed shut, the engine could get hot and bothered.  Why DSGs have 2 thermostats.....I couldn't tell you......either way, the engine is grumpy and needs cheering up with some fresh parts.

[LC5F]

I could be wrong, but I believe the front temp sensor is for fuelling compensations, being in the water pump output flow, and the gearbox side one is for triggering the fans/dash temp gauge as it's the output from the radiator.

Is your car a DSG?  I believe they have an extra thermostat in the temp sensor housing, above the gearbox housing where LC5F mentioned.  Could this be stuck shut perhaps?  Manuals only have the main stat at the front.

Yes - they do different tasks, but if I recall correctly its the one mounted in the thermostat that runs the fans - Mine had fans on all the time - changed the sensor over the gearbox - no change, had to take out the thermostat that I only fitted a few months before and the fans stopped randomly running.

Inline DSG thermostat is usually open, I can only assume to allow some flow rather than none.
Pretty easy to change, just be careful squeezing past of the pipe connector like this:

The small tube snaps really easily...dont ask how I know.
If your quick with your hands and get the pipes just nearly off you can change them without losing too much coolant.

[Cizx]

Ok ill have to keep that in mind i will also keep this post updated as i go but today i ran the ac to see if i could get a light to come on no light BUT i did notice my car started running extremely rich when i kicked on the ac started to sputter pretty bad under moderate acceleration so if one sensor is for fuel compensation there could be a chance its at least part of the problem and to be fair this car has 175000 miles (282000 Km) and im the third owner so its probably safe to say no one really took the best care of this car

[LC5F]

To me third owner suggests it was well cared for by at least one of the previous owners - your just unfortunate to catch the wear from age and mileage.