A6 heating running cool

[gazza57]

Hi,
I have a 2.7t A6 and recently, I've noticed that the cabin is not as warm as it should be, when I start, selecting say 21c will start the fan running, but the air is distinctly tepid, not cold.
If I wind up the temp to HI when the engine is fully up to temperature the fan speed goes up but the air is distinctly cool.
My first thoughts are cabin temperature sensor, I think there's one in the front of the AC unit, but are there any others and if so does anyone know where they are?
I have recently had the fault codes checked because of a misfire which showed a faulty coil pack which I have just replaced.
Does anyone know if the fault codes for all modules show up when scanned?
the engine management one picked up the faulty coil pack but would you need to go into the AC module on the scanner to see if there was an AC fault code or are they common?
Thanks
Gazza57

[djl78]

Hi,
I have a 2.7t A6 and recently, I've noticed that the cabin is not as warm as it should be, when I start, selecting say 21c will start the fan running, but the air is distinctly tepid, not cold.
If I wind up the temp to HI when the engine is fully up to temperature the fan speed goes up but the air is distinctly cool.
My first thoughts are cabin temperature sensor, I think there's one in the front of the AC unit, but are there any others and if so does anyone know where they are?
I have recently had the fault codes checked because of a misfire which showed a faulty coil pack which I have just replaced.
Does anyone know if the fault codes for all modules show up when scanned?
the engine management one picked up the faulty coil pack but would you need to go into the AC module on the scanner to see if there was an AC fault code or are they common?
Thanks
Gazza57

Could be sensors or one or more of the positioning motors on the heater control flaps.Ideally you should get vehicle scanned for fault codes,in particular HVAC (Heating,Ventilation &Air Conditioning) module.
djl

[Peter D]

Year and model. I assume the engine temp rises as normal and is stable. Is there plently of air flow. ?? Check the pollen filter is not soaked or disintergrated and fallen into the blower. The two side of the car can have sepaerate temperatures so two sensors, are they both the same temp. HVAC ECU needs to be read for error cades, this could be a number of things but a flap motor is often the cause. PM me your email address and send you the diagram. Regards Peter

[paul b]

You can check the HVAC with VAG-COM.

IIRC, there is a temperature sensor not too far from behind the nearside headlamp, which may cause this sort of fault. However, a VAG-COM scan would usually explain if that sensor is at fault.

I'm sure I saw a thread a while back about such a sensor... I'm sure someone will say if I'm talking poo...

Paul

[gazza57]

Scanner showed no fault codes, but I have discovered that one of the two pipes going into the heater matrix which should both be hot is cold.
One is hot and one is cold which suggests low or no flow through the matrix.
We are going to try to back flush out the matrix to see if any crud comes out, if not and it's still blocked then it's new heater matrix which I think is dashboard out....groan!
Gazza57

[gazza57]

Further developments,
Flushed out the matrix no appreciable muck inside, it is not blocked, have changed temp sensor on matrix outlet, still cold.
There's no valve in the heater box so I cant understand why its not flowing through the matrix.
suspect temp sensor inside the cabin, the one on the ac control unit in the centre between the two temp selectors.
Can't think of anything else now, just as well change it have spent pounds and pounds changing other sensors still no bloody good

[Peter D]

The sensor contols the flap motor thus contolling how much air travels through the matrix noy how much water goes through the matrix. Diss-connent the output pipe from the matrix clamping off the pipe and fire the car up, does coolant flow through the matrix. It so then plug the matrix and release the clamp and fire the car up and loosen the clamp does coolant come out of that pipe. ?? I've sent you all the diagrams already. Regards Peter

[gazza57]

Thanks Pete,
The diagrams will be a real help, we will do what you suggest, they flushed the matrix through last week and it was completely clear, water flowing in and out both clean, no crud.
It only seems to stop flowing when it's connected back into the coolant circuit.
Also no fault codes appear to be generated in the HVAC module,the engine runs up to temperature and certainly doesn't run hot which I imagine it would had there been a blockage somewhere else.
Nonetheless we will do as you suggest again and see what happens, your efforts Peter are much appreciated, thank you again buddy!
Gazza57

[gazza57]

All sorted now, the heater ran cool for a while after we boxed it up but as time went on it got better and beter and now it's fine.
Thanks to PeterD for all his help and drawings and of course his time!
Gazza57

[wibers]

Hi,

I seem to be having the same problem. Is there any chance of a copy of your drawings??

Thanks

Wibers