Intermittent Climate Failure

Hello diesel mechanics,

I have an Audi 80 B4 TDI, and for some time now, the air conditioning has been failing while I'm driving.
My initial suspicion was that the air conditioning system hadn't been serviced in a long time and therefore contained refrigerant that was no longer effective. As a result, I had it refilled.
Unfortunately, it didn't help. It's not possible to access the climate control unit's control module using VAG-Com.

Following a test, it was determined that the climate control system only fails above a certain torque level. Therefore, the climate control system functions perfectly well when the engine is idling, even if the engine speed is manually maintained at 3000 RPM for a few minutes.

It only works while driving, because the car is running in a low-power mode.

If I'm not mistaken, the compressor in this old TDI is still controlled by the engine control unit.
Does anyone have any recommendations for other things I could watch?

Greetings.

The compressor's magnetic coupling is likely worn out.

Quite a far-fetched speculation: when driving at full throttle (pedal pressed all the way down), the air conditioning might be turned off (at least during peak loads). Perhaps someone 'tinkered' with the vehicle's system, unknowingly changing the switching threshold. This should be in the data set, right? Rainer

First of all, thank you for the tips.

The engine control unit (ECU) has not been chipped.
If the magnetic clutch is worn out, why does the air conditioning still work when the car is stationary? You can rev the engine and do whatever you want, but the air conditioning doesn't turn off.

When the car is driven, the compressor shuts off at approximately 2500 RPM if more torque is requested via the accelerator pedal. The disengagement of the compressor can also be heard through a relay clicking. When the accelerator is released, the compressor is re-engaged, but only if the time elapsed does not exceed approximately 10 seconds.

When the car is driven, the compressor shuts off at approximately 2500 RPM if more torque is requested via the accelerator pedal. The shutting off of the compressor can also be heard through a relay clicking. If the accelerator is released, the compressor is re-engaged. However, this only happens if a period of approximately 10 seconds is not exceeded.

That clicking sound could just as easily be coming from the AGR valve - it sounds similar.

Perhaps try connecting a 12V light bulb or a voltmeter to the wiring leading to the magnetic coupling to check it.

I hear a clicking sound inside the car. I've already removed the panel under the dashboard. The clicking is coming from the climate control unit.

I hear the clicking sound inside. I've also already removed the panel under the dashboard. The clicking is coming from the climate control unit.

The clicking sound is the relay that powers the clutch for the clutch engagement.
However, there are two additional switches that prevent the clutch from engaging.

The fan is controlled by the refrigerant pressure. If this does not help to reduce the refrigerant pressure, the system will shut down (although the fan will run at full speed before this happens).

There is also a defrost switch that turns off the system when the evaporator becomes frosted, which indicates that the cooling capacity is too high.
And it's precisely in that area, or in that environment, that I expect the error to occur.
If the engine power is low, the cooling capacity is not sufficient to cause freezing, so everything is okay.
At higher speeds, regulation is needed. However, this regulation is not happening (which is the source of the problem), and the Evaporator is freezing up.

Or the anti-icing switch has lost its activation threshold.
Okay, check the NTC Evapora_Out (air behind the evaporator) and test the anti-icing switch...

Then we'll see.

Best regards, Jochen.

I have to admit that I'm not very knowledgeable about car parts, so I've probably never heard of a part called an 'Evapora' before.
However, I am almost 98% certain that there are no more electrical components after the vaporizer. Are you sure that every air conditioning system has this design?

Furthermore, this diagnosis would mean that the evaporator freezes very quickly. In my case, it happens within 2 seconds, because as soon as I don't approach it very carefully, the air conditioning immediately shuts off.

My suspicion leans more towards the engine control unit (ECU), as I read in the wiring diagram that the compressor is controlled via the ECU.
However, VAG-Com displayed an error message.

Do the radiator fans run when the air conditioning is on?

Sorry, I can't help you with that. But that assumption you made about the engine control unit sounds familiar to me.

If I understand correctly, for example, a VW VR6 with an automatic transmission actually has a disengagement of the clutch via a magnetic coupling during kick-down. However, I don't know whether this comes from the transmission control unit or the engine control unit.

Both climate control fans initially run at half speed when the car is stationary, and then switch to full speed after approximately 10 seconds. This was also tested by connecting the fans directly, and the fans and the control unit are confirmed to be working correctly.

My G IV also turns off the compressor if you accelerate with more than about half throttle. It doesn't even take a kickdown to do it.

Perhaps there's something useful in the compressor deactivation conditions described in my article (the question is, which of those conditions the Audi can actually implement).
I'm sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.

Quote:

Shutdown code Compressor shutdown condition. 0 None. 1 High-pressure event. 2 faulty bulbs + Uist <3V> 118°C. 12 Motronic interfaces. Page 13. Terminal 15: 17V. 14 Function: Evaporator temperature. 15 without vehicle coding. 16 Comp. amps. 17 Drucksensor def. (nur mit ext. gereg. Compressor) 18 Engine speed (only for B5W8)

Based on how I'm interpreting the reports, the potential candidates are:

- a faulty interior blower fan.
- High external temperature reported.
- Engine overheating (faulty sensor?)
- The Motronic system is constantly reporting values above half throttle, indicating a faulty switch.
- Overvoltage in the vehicle's electrical system.
- Evaporator is frosted (see blower).
- Voltage to the compressor magnetic coupling too high.

The problem here is that the climate control module isn't sending out any error messages.

T2-TDI wrote:

Both climate control fans start at half speed when idling and then switch to full speed after approximately 10 seconds. This was also tested by connecting them directly, and the fans are working correctly, as is the control unit.

Running at full load is rather unusual at such an early stage; with my tractor, I only reach the second stage a maximum of 1-2 times per year . In our (gasoline-powered) Polo, it takes more than 10 seconds after turning on the air conditioning for the fan to even start.

Okay, even though the air conditioning system has failed, the fans are still running at full speed. Additionally, the air conditioning can only be reactivated by turning off the ignition and then turning it back on. Therefore, it's not possible to simply turn it on and off using the control panel.

Roger wrote:

Running at full load is quite unusual at such an early stage; with my tractor, I can only reach the second level a maximum of 1-2 times per year.. In our (gasoline-powered) Polo, it takes more than 10 seconds after turning on the air conditioning for the fans to even start.

.

"Sometimes, the fans in my GIII VR6 turn on to the second speed level when the air conditioning is on, even though the coolant temperature isn't even high enough to trigger the first speed. However, I've already replaced both the fan switch in the radiator and the brown temperature sensor for the air conditioning in the coolant regulator housing. Therefore, I don't believe it's a problem with those components, and if there is an issue, it's more likely related to the air conditioning system itself. I'm talking about a manual air conditioning system."

T2-TDI wrote:

With VAG-Com, it is not possible to access the control unit of the climate control system.

Yes, the manual climate control system in that vehicle is actually diagnosable!
see here

T2-TDI wrote:

If I'm not mistaken, the compressor in this old TDI is still controlled by the engine control unit.

No, there's a separate control unit located behind the storage compartment under the steering wheel. It's quite inconspicuous and looks like an oversized relay.

Read the error codes; they will tell you exactly which condition is causing the air conditioning to shut off.