Peculiar HVAC issue - no air but blower works?!

If you switch off the A/C controller, the blower will not run. So removing fuse 38 will also stop the blower.

RAB
 
If you switch off the A/C controller, the blower will not run. So removing fuse 38 will also stop the blower.

RAB
Not sure if Fuse 38 supplies the Climatronic Controller as well as the AC, don't have a cct diagram. The Climatronic Controller does more than just control the AC, so may be fused independently.
Does anyone know?

Mac.
 
F38 supplies the controller, which is connected to the blower control unit. I have checked the circuit diagram.

RAB
 
Interesting thought about the AC and N280 valve. When pushing ECON mode today, the air came back instantly. Heat as well. I could swear this was not the case a couple of days ago. That would suggest a flap issue. Will pursue further this weekend.
 
Strange how, assuming pressing ECON reduces N280 flow >2%, and hence no refrigerant through Evap (so no AC) , can affect airflow. Can't imagine iceing on Evap could clear that fast. As you say, instant flow points to flaps, but air flow is controlled by Blower speed, not flaps.
Could remove the compressor belt to stop aircon I suppose, as RAB's info makes pulling a fuse a non-runner.
Will sleep on it!
Mac.
 
When pushing ECON mode today, the air came back instantly. Heat as well.
Was that with a hot or cold engine? Don't forget that you have two sources of heat, the electric heater and the normal heat exchanger. The former will supply heat at start-up (but not with ECON on) and the latter will take over when the engine heats up. However, with AUTO selected, if the heat exchanger does not heat up, the blower will run slowly.

Are you sure that you didn't switch ECON off, thereby enabling the electric heater which would also speed up the blower?

RAB
 
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The AC is controlled by means of regulating valve N280, which is continuously variable via PWM (Pulse Width Modulation), so, not just open or closed. The HVAC (Climatronic) Controller controls the N280 valve. So, if it fails open, AC is on, and uncontrolled.
These circuits are usually (or should be) designed to fail safe. So A/C would be off with such a failure.

RAB
 
These circuits are usually (or should be) designed to fail safe. So A/C would be off with such a failure.

RAB
RAB, I was thinking of a mechanical failure of the N280 valve, so the control circuits would think it was (nearly) closed when it wasn't. But, you're probably right, something somewhere would spot an anomaly, and flag an error code.
Mac.
 
Hi guys! Love all the great comments. I am scripting a label file for the HVAC measuring blocks (controller 08) so I can make measurements when the car is mobile. Actually an intermittent fault code appeared today!! N280 short to positive. That implies what some of you did suspect early, that there is something strange going on with the evaporator/AC.

In the weekend I got lucky and spotted a newly decomissioned A2 at the breakers. I was able to salvage all the servos and temperature sensors from the HVAC. Also the high pressure sensor from the AC. I had some misfortune though when pulling out the N280 from the compressor. There was still pressure in the system and the valve shot out into the ground and got covered in sand. Don't think I can use it. I managed to pull another n280 from a skoda fabia. They seem to be the same part.

Of course I will share the label file if it results in something useful :)

cheers
.s
 
In the meantime I run in ECON mode and the airflow is perfectly fine. In the workshop manual there is some fine print in the measuring blocks section regarding fresh air flap movement. There is a mode called Air Flow Mode which closes both the fresh air flap and recirculated air flap at the same time when driving over 80 km/h. Maybe this could also contribute to my problem.

"The following air conditioner operating statuses are possible via the levers fitted on the flaps depending on the positioning motor setting:

- Fresh air flap closed and recirculated air flap open = Recirculated-air mode
- Fresh air flap open and recirculated air flap closed = Fresh air mode (feedback value in display zones “1” and “ 2” between “135” and “145”).
- Recirculated air flap closed and fresh air flap closed = Air flow mode. The position of the fresh air flap is program controlled in air flow mode. Depending on vehicle speed, the fresh air blower speed, the selected and actual temperature readings and the selected operating and display unit for air conditioner/Climatronic -E87- mode, the flap is closed from a speed of approx. 80 km/h. However, the fresh-air flap is not completely closed in air flow mode (it always remains open far enough to maintain the necessary air throughput)"
 
Good stuff, I'm thinking that the the " necessary air throughput" that the the partially open flap allows, is necessary because their is always a flow, (albeit >2%), of refrigerant through the evap. If there was no flow the evap would get very cold indeed, and, probably ice up. This is independent of ECON or AC mode (no AC compressor clutch, just the N280).
So, maybe in AC mode, your flaps/servos/position sensors get confused, and reduce air flow, but do not move the N280 to minimum.
Can you include (road) "speed, the fresh air blower speed, the selected and actual temperature readings and the selected selected operating and display unit for air conditioner/Climatronic -E87- mode" in your script?
If possible two runs, one in ECON, one in AC, might well show what's going on.
I'm really enjoying following this investigation.
Thanks for sharing, and good luck.
Are there any guides to writing VCDS scripts online?
Mac.
 
Good stuff, I'm thinking that the the " necessary air throughput" that the the partially open flap allows, is necessary because their is always a flow, (albeit >2%), of refrigerant through the evap. If there was no flow the evap would get very cold indeed, and, probably ice up. This is independent of ECON or AC mode (no AC compressor clutch, just the N280).
Don't forget that the A/C switches off at something like 5 to 7deg C to prevent icing. ECON also switches off A/C, as well as the electric heater. There are other factors that switch off the electric heater, such as the load on the alternator.

RAB
 
Don't forget that the A/C switches off at something like 5 to 7deg C to prevent icing. ECON also switches off A/C, as well as the electric heater. There are other factors that switch off the electric heater, such as the load on the alternator.

RAB
RAB,
AC never actually turns off on the A2, the compressor is driven directly, with no clutch. If the engine is running, so is the compressor. So, refrigerant is always circulating through the evap. The N280 should, with ECON on, or when the Climatronic Controller says so, reduce this flow to >2% of max. If there is a problem with the N280 or the controller, that refrigerant flow could be <2%. That would, probably, cause the evap to ice up.
Mac
 
It's very doubtful that icing would occur at less than 2%; that's why it effectively shuts down at the above temperature. The system would be designed not to freeze up, under any circumstances.

RAB
 
I now have a preliminary label file for the HVAC measuring blocks on the A2. Tried it when driving to work the other day. Everything seemed nominal. Even the N280 and AC pressure values. But this day it was cold, about 5 degrees. I think the period with obstructed airflow was a bit warmer, around 10-15 degrees. Maybe I will have to wait for spring to get a full conclusion :)

I will make some corrections in the label file and post it here afterwards. I guess rosstech would like a copy as well.

@PlasticMac There are instructions in the template label file that is in the VCDS program folder if you want to write some ;)
 
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Forgot to point out: During my trip to work the car never got into "air flow mode" but stayed in "fresh air mode" the whole time. Speed 110 km/h. N280 off (current 0.010A) Pressure in AC system only 3 bar (means that it is off). Fresh air intake temp 5 degrees. Evaporator output temp 4 degrees. Heat flap moving from full heat to a moderate mix with cold air during trip as expected. ECON did only switch of the aux heater and did not affect the AC that was off the whole time.

Massive amount of HVAC geek points in this post ?
 
This has all the symptoms of a failed G263:


RAB
 
Good find RAB. Failed G263 = Evap icing up. Hope this helps sunebralla.
I find this thread interesting and informative.
Vorsprung indeed!
Mac.
 
G263 should leave an error code. If wire is broken it will think it's already freezing. Had to change mine and looking at it, the most common failure was and should be wire breaking due to vibrations, since it is a long sensor. Bending it while measuring revealed broken wire near connection. If sensor somehow slightly shorts or goes bad, it should show high temp on vcds under measuring blocks. Either way temperature should look out of place or leave code (unless it shorts only in humid weather or some other rare instances).
 
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