A4 8E AC Not Cooling: Causes & Fixes

Hello!

Hardware: A4 8E, year 2001, 91,000 km, AWX engine, FEC.

Problem: The timing chain was recently replaced, and now the automatic climate control is no longer cooling. I suspect a connection, as the entire front of the car is put into service mode during the replacement, but I haven't been able to identify the cause. (All the connector connections that I could reach from above seemed to be okay.)

Investigated:

-> The air conditioning system was refilled mid-last year, and it was working perfectly until recently.

-> Actuator diagnostics ran without problems, no error entries, -> OK.

-> All accessible circuit breakers for the air conditioning system have been checked and are functioning correctly.

-> The A/C compressor is also driven by a ribbed belt, which has the correct tension. (However, this compressor does not have a magnetic clutch, but a wobble plate, so I don't know how much it actually 'engages').

-> Battery disconnected for 10 minutes, -> problem not resolved.

-> All flash storages read, no errors found.

-> No unusual noises during engine operation, and the heating function is also working perfectly.


Interestingly, the motor windings appear to be fine during operation. When in 'ECON' mode, the system draws 0.0A of current and operates at 0.0% load. Disabling 'ECON' mode increases the current draw to approximately 0.6A, and in the case mentioned, the load increases to 64%, but the system pressure remains constant at 6-7 bar.
When I compare this to my A4, the pressure should increase from 6-7 bar (ECON mode) to a good 12-14 bar (non-ECON mode), but it doesn't.

And the question now is, why not?

If the pressure is too low due to a coolant shortage, there should be an error message. However, 6-7 bar is the same pressure as what I have in my A4, and it works fine there.
If a sensor is not connected, this should also be reflected in the system status.

At the condenser inlet, located in front of the engine radiator, you can feel that something warm is being pumped in, but the area that feels warm is only about the size of your palm.

Thank you for your help!

Hello,

Is the swashplate really okay? Because in some cases, you can't see from above when the rubber has detached from the plate, and therefore a proper power transfer can no longer occur.

Otherwise, if everything else seems okay, I would say that there might be too little refrigerant.

Best regards, Christian.

'Regarding the impeller in the compressor, I can't really assess that. However, the drive pulley for the ribbed belt is running very smoothly, and it's also turning the shaft that goes into the compressor.'

If there was a lack of coolant, wouldn't that trigger a fault code (FS) due to insufficient operating pressure?

Especially... just 3 years ago, there was only an 8% shortage of refrigerant. Therefore, it's unlikely that 'all' of the refrigerant was lost during the 2-week period surrounding the compressor replacement.

Do you have approximately 6 bar on both the high and low pressure sides?

If that's the case, the compressor definitely isn't building up any pressure. With a properly functioning compressor, you should have approximately 2 bar on the low-pressure side and around 8 bar on the high-pressure side, depending on the operating conditions.

Are you sure you already have a compressor with a pressure relief valve? Or does it have a magnetic coupling? With a compressor that has a magnetic coupling, the green connector to the compressor often comes loose after the front panel is in service mode. I've seen this happen multiple times!

Regards,
Sure, here is the translation of the text from German to English:

"Micha"

Are you sure you already have a compressor with a pressure relief valve? Or does it have a magnetic coupling? With a compressor that has a magnetic coupling, the green connector to the compressor often comes loose after the front panel is in service mode. I've seen this happen multiple times!


So, with the 8E model, self-regulating compressors were used across the board, and these compressors operate without a magnetic coupling.

Since the vehicle is not currently within my reach: Could it be that the connector for the compressor mentioned above is disconnected, or that a connector is present? Because you seemed to be focusing on the magnetic clutch...

'So, the vehicle was in the workshop today, and the swashplate is definitely worn out, and the rubber coupling has failed. This means the compressor is defective or seized.'

Now, my suspicion is that, since the system was working perfectly before the refrigerant change and the compressor wasn't making any noise, there's a connection to the refrigerant change. The workshop is simply dismissing it as a coincidence, but I find that implausible, as I've never seen anything like it. It was 100% okay and then broke, and that happened right before/after the refrigerant change. The system is leak-tight and completely filled.

Could it be that?

- Der eine Keilrippenriemen zu fest gespannt wurde und daher die Lager im Kompr. festliefen? Normal ist ein autom. Dämpfer (Federelement) der soetwas verhindern sollte. Idea?

- Can the compressor be damaged if it is accidentally turned back slightly during a refrigerant replacement, i.e., against its normal direction of rotation?

Normally, the compressor remains attached to the engine block, but I still need to check if they may have removed it and reinstalled it in a different location.

The part is actually expensive... €800, including installation.

'Another question: How can I check if only the coupling is defective and the compressor shaft can still rotate, indicating that the compressor itself is okay, when the pulley is detached (as mentioned above: the rubber coupling is detached)?'

There were some compressor intermediate pressure sensors installed in the 8E (part numbers 8E0 260 805 N, M) where the clutch would engage due to rough engine running, and only the clutch itself would be defective. There's already an improved pulley (part number 8E0 260 805 AB) available as an aftermarket part for around €150.

Okay, the vehicle has just undergone a quick inspection.

The pulley seized (but it was a 'D' version, not an 'A' version as indicated by the expert, and a rather old, unreliable model). However, the compressor shaft can be easily turned in the direction of rotation with a finger, without making much noise.

The compressor was not removed, and I would like to know how they could diagnose a 'failure' at the workshop. Furthermore, they forgot to reinstall several screws of the underbody paneling during the reassembly...

Is it okay that the pulley rotates so easily, and could we confidently rely on replacing the pulley to fix the issue?

Hi,

Here's my opinion: If the rubber band slips, something must have been blocking it, even if only for a short time. However, if it were my car, I would first try replacing the pulley. As long as the compressor's input shaft doesn't break when removing the pulley. Keyword: oxidation.

Best regards, Christian.

My opinion on that: If the tire tread separates, something must have blocked it, even if only for a short time.

So, D is the ancient disc...

D -> N -> M -> AB

For all indices preceding AB, the clutch can be engaged due to two reasons (incorrectly, therefore all are replaced!).

- Uneven engine running.
- Compressor shaft blocked.

Zweiteres scheidet def. aus (Welle läßt sich so leicht drehen, wie wenn man mit dem Finger einen Bierdeckel übern Tisch schiebt ), ersteres ist möglich nach ZR Wechsel, def. PD-Element, etc.
Today, there's definitely smoke in that workshop...

Is the ease with which the compressor shaft rotates really an indication that the compressor is working properly? Based on what I've read about compressors, shouldn't the pistons inside the compressor only start moving when a swashplate is engaged? This would mean that without the swashplate engaged, the pistons shouldn't move, and therefore the shaft should rotate freely. Only when power is required does the swashplate act on the pistons, which would then cause the rotation to become more difficult, or in the case of a malfunction, it would seize up.
It's just a thought and my conclusion based on what I've read about the air conditioning system. I hope I haven't misunderstood anything.

Well, almost!

The wobble plate roughly changes the displacement volume of the compressor, and thus its power output. When the engine is off, the wobble plate goes to 0 displacement, which corresponds to about 2% of the power. During startup, the power is gradually increased to avoid shocks to the belt drive, as was the case with the old magnetic couplings.

Do the compressor bearings have a seizure? Is nothing rotating, or is everything extremely difficult to turn?

By the way, the workshop has been quite accommodating: After some rather frustrating 'wake-up calls' yesterday (they didn't even know that the pulley could be replaced individually. Seriously?), they are now, as a trial, replacing the pulley free of charge, including labor. If that doesn't work, they will replace the entire compressor free of charge.