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AC not working after refill


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I have just been to a shop where they have this filly automatic AC service machine to refill my AC system.

 

I had the following fault code shown in vcds:

0029 - Refrigerant Pressure

002 - Lower Limit Exceeded

 

So the  guy hooks up the machine, it takes 30 or so minutes to do its thing and then they say it needed a complete top up and that there is no leak. Fine. Then we do a test, turn the climate control to full blast and ECON off, the car still blows hot air....

 

There is a slight change of tone in the engine at idle when you turn the AC on (ECOn off) and the fans seem to start up as soon as the AC is turned on. Quite normal, right? But, I remember from my father's mk1 that when he turned the AC on, the fuel consumption would change from 0.9 to 1.1/1.2. Mine seems to stay at 0.5 regardless if its on or off...

 

The guy who ran the machine said I should try and change the pressure sensor to start with. I am far from being an expert on this but does it make sense or am I looking at a potential compressor change? 

Went back to my mechanic, he took the aux belt off, spun the compressor wheel and said its all fine and also mentioned the compressor looks like it has been changed not so long ago (I only had the car for 10 months now). I know there are many topics about AC out here and having read many of them already I can't seem to be able to fall into any of the already discussed scenarios.

 

PS: Where is the pressure sensor located? is it an easy change?

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Don't know - I will scan it again as soon as I get home. 

 

I would assume if there is no change and I still get the same error, the sensor is faulty. Shouldn't there be a fault code for the sensor itself?

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3 minutes ago, Inex said:

Don't know - I will scan it again as soon as I get home. 

 

I would assume if there is no change and I still get the same error, the sensor is faulty. Shouldn't there be a fault code for the sensor itself?

That is exactly what I would be thinking. 

 

Yes, there maybe a fault code for the sensor but depending on how it goes faulty I suppose it "may" not register as a fault.

 

I'm not an expert on AC, so see what other's post too.

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Just ran another scan now that I got home:

 

0029 - Refrigerant Pressure

002 - Lower Limit Exceeded - Intermittent 

 

...so it changed to intermittent. I delete the error and it never comes back. Took a 10 minute drive and there is still no fault in the HVAC... AC still blowing hot air...

 

I tried disconnecting the sensor (thinking I would somehow reset the sensor) - got the Open circuit fault, then connected it back on and erased the error - all clear no faults.... still AC blowing hot.

 

I tried going into the Measuring blocks and the Refrigerant pressure fluctuates between 8 to 10 bar. Don't know if this is normal or not. It would be nice if someone with a working AC could read this for me and tell me what it shows. it's Group 003 on the Auto HVAC.

 

 

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When you say hot air do you mean high temperature or ambient temperature. If it is genuinely HOT then you may have a failed air mixer flap valve in the Climatronic/ heater unit.

 

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Don't know really... It was quite warm and sunny that day.

 

Stuck a thermometer in the vent before starting up and it showed 27C with the doors and windows closed. Then we turn the AC to full blast and the air blown in was fluctuating between 26 and 27 degrees. Now I doubt the outside temperature was really 27 but we did all of this in the sun.

 

How do I figure out if its genuinely hot or just as cold as the non conditioned cold air would be? To the hand it feels like there is no difference between AC on or AC off when running full blast. It is certainly not as hot as when you turn the temp to High.

 

Also, I kept the AC on on the way home (28 km drive) and there was no significant increase in fuel consumption. I would expect a bit worse of an economy with the AC ON even if I didn't get any cold air. Does this mean anything?

Edited by Inex
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I don't have VCDS so can't tell you what my measurements are.

 

Can you feel cold on any of the low pressure pipes with aircon running. Maybe where they enter the firewall? Careful not to touch moving / hot engine parts / fans.

 

Does this thread help at all? Some reference data in there.  Possible N280 problem or wiring to?

 

 

I'm sure some others with more knowledge than me will reply when they next review.. 

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1 hour ago, TheClient said:

I don't have VCDS so can't tell you what my measurements are.

 

Can you feel cold on any of the low pressure pipes with aircon running. Maybe where they enter the firewall? Careful not to touch moving / hot engine parts / fans.

 

Does this thread help at all? Some reference data in there.  Possible N280 problem or wiring to?

 

 

I'm sure some others with more knowledge than me will reply when they next review.. 

 

I will try get a readout of my data blocks and compare them with the "healthy one" posted here.

 

I have also gone further down the thread and got onto this one:

This seems tempting to try, especially because I have no vcds errors anymore.... but where to get the part from?

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If I stick a socket onto the main bolt holding the compressor wheel and try to spin it clockwise, will that tell me if the compressor shaft is ceased? If it were ceased, the bolt would not be rotating when AC is on and engine is running, correct?

 

Do I need to take the aux belt off for this?

Edited by Inex
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5 minutes ago, Wino said:

In your VCDS measuring blocks, is there one called compressor shutoff code? What number is in it when A/C is running?

Will connect to the car soon and I will post all the parameters here.

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11 minutes ago, Inex said:

If I stick a socket onto the main bolt holding the compressor wheel and try to spin it clockwise, will that tell me if the compressor shaft is ceased? If it were ceased, the bolt would not be rotating when AC is on and engine is running, correct?

 

Do I need to take the aux belt off for this?

I think the whole pulley including that central nut/bolt should spin as one. 

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Compressor shot off code: 0.0

Engine speed: 800/min (matches engine speed as I rev it up

Compressor current (actual): 0.825A

Compressor current (specified): 0.820A

COmpressor rotations: 1000 (matches engine revs)

Compressor load 1.2 Nm

Refrigerant Pressure: 5.4 bar

Radiator Fan activation (actual): 9.6%

Radiator fan activation (spec): 0.0%

 

Edited by Inex
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OK, pretty sure the 0.0 means the control electronics is happy with everything and has enabled the compressor, but the refrigerant pressure of 5.4 bar suggests it isn't achieving any compressing. I think when running on my Polo, the pressure is maintained in the 10-15 bar range by the radiator fans cutting in and out.

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Yesterday was about 9 bar. It was actually fluctuating between 7 and 9 that was after having run the compressor for half an hour drive. 

 

So I suppose this is a bad compressor?

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I'm afraid I'm running out of ideas and don't want to cost you money by suggesting you swap parts without really knowing what I'm talking about.  Wait for other input. :)

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Just made a comparison of the data blocks with my work colleague who drives a petrol VRS and has a fully functional AC.

 

The differences are as follows:

Compressor load: 5Nm at idle as opposed to 1.2 on mine...

Refrigerant Pressure fluctuating between 9 and 11 bar as opposed to never getting higher than 9 on mine.

 

What I also noticed is the following:

- One of the pipes while the AC was running is really cold as opposed to mine where both pipes are ambient temperature.

 

Would this be a clue for anything?

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Well, it seems to rule out a mixer flap problem in the cabin, as if there is no cold being provided by the refrigerant and compressor in the evaporator, you can't get cold in the cabin by mixing cold and warm air...

 

Further than that I don't really know.  The loading looks much lower and perhaps consequently, the pressure looks a bit low, but perhaps not so low for no operation at all?  If i'm reading it right, your previous data indicates there is the specified current going to the N280 regulating valve, unless it is stuck. I don't have any more solid ideas of where to take this.

 

See if others do.

 

Edit: Just reading through the link Wino sent for VCDS tips, in the notes it suggests checking the supply to the N280 with an incandescent light. Not sure if that is significant - as couldn't they have just said check actual and specified current readings? Maybe worth a test, if it lights, I guess it is looking more like the regulating valve / compressor. 

Edited by TheClient
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Will the high pressure line be cold if e280 valve is stuck?

 

Any idea if any valve would fit or should I look for a HELLA valve like the compressor?

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