Engine Misfire with Working Climate Control

Hello!

I've observed a peculiar and, for me, new phenomenon over the past two days:

Yesterday, at an outside temperature of 38°C (Climatronic set to 'Auto' at 20°C with the fan at 4 out of 6), and during extreme stop-and-go traffic, the engine started to stutter and jerk, both when idling and when starting to accelerate.
The jerking is clearly noticeable and can be seen in the tachometer needle; when starting, the vehicle actually rocks back and forth. In neutral and when giving it gas in neutral, a shaking occurs approximately every 6-7 seconds. The engine speed then fluctuates back and forth in three bursts, by up to (estimated) 50 RPM. The air conditioning fan ran continuously, and occasionally the radiator fan also turned on (which I had never seen before).
I then opened the hood and observed a clicking sound coming from the compressor, synchronized with the shaking. Everything returns to normal when the air conditioning is turned off or the engine is revved up.

Is there possibly a safety circuit that shuts off the compressor if the temperature of the refrigerant (or even the engine coolant) exceeds a maximum value?
Could this happen at such short intervals that the engine would then fall into a regular pattern of jolts?

Thank you for the tips and guesses...

My mill*) experiences vibrations, even when idling, which originate from the belt drive, especially in extreme temperatures.

As soon as I switch to gear N, it starts, and it's very easy to reproduce. It starts when it's really hot outside AND the radiator fans switch to level 2 after a short period of inactivity. Then, the air conditioning compressor and alternator put a lot of strain on the belt. The interior fan usually also turns on to wind speed 10.7 .


Here's an interesting point: the fan control seems to be calculated, because you can force it to switch to level 2 (full fan speed with 'LO' = high cooling demand) or avoid it (fan at its lowest speed with 'LO' = low cooling demand). The temperatures (oil and coolant) only fluctuate within a degree range, meaning within the resolution of the analog-to-digital converters. The pressure in the air conditioning system is not being measured. The fan turns off completely immediately when the 'ECON' button is pressed, so there are definitely no heat-related issues. Does anyone have more detailed information regarding the software in the Climatronic and the fan control unit?

CU Gremlin.

*)
Octavia ALH automatic - climatronic.

@Gremlin

As far as I remember, the process is as follows: Air conditioning on --> Climate control temperature switch for fan speed level 2 --> Fan control unit.

Therefore, it is clear that when the climate control (ECON) is activated, the fan turns off even though the climate control is still producing hot air. This suggests that there is a thermal component involved, rather than a purely calculated one.

--> Think simple!


@Guys
There's an over-temperature sensor in the AC system that, in my opinion, shuts off the compressor. However, I don't think that matches your six seconds. I would expect that interval to be longer. (But, as often, I don't know the exact details ).


Regards,
-Private

@Friends:

The compressor will definitely not be cycled on and off (intentionally) within the short interval you mentioned. These types of compressors avoid rapid on/off cycles because the high pressure spikes would cause excessive mechanical wear. In large installations, time locks are also built in, typically in the minute range, which also prevent manual activation for a certain period. Furthermore, the high cooling capacity required in the situation you described would also prevent cycling.

Several potential causes for the error are possible.

- Under- or over-voltage in the vehicle's electrical system (weak battery, faulty voltage regulator), in my opinion, the most likely cause.
- Compressor current too high.
- Engine temperature slightly above/below 118 degrees.

Is your CT scanner diagnostic?
If so, what does the memory say?

Have you ever checked channel 19 (compressor shut-off condition)? It works on my Golf from 2002, but it might not work on older models.

@Roger

Thank you for the tips!
I've now paid closer attention to this phenomenon, and it's absolutely reproducible; the higher the outside temperature, the faster it happens.

I can't rule out the battery; it's about 4 years old and has 100,000 km (approximately 62,000 miles) on it. Additionally, for the past six months, it's been starting a little slower when it's warm (possibly due to a reduced starter motor speed caused by a weak battery).

I hope the engine temperature doesn't exceed 118°C, as it's just stop-and-go traffic, meaning no load or high RPM. It's simply extreme congestion and an outside temperature of 40°C.
If I remember correctly, I can at least check the battery voltage using VAG COM, and I will do that. I will also test whether my CT is diagnostic-capable, although the car is from '99.
'Normal' deactivation is definitely not possible, because the car rocks so much that it becomes IMPOSSIBLE to start smoothly in first and second gear. However, as soon as I lower the fan speed or reduce the desired temperature to 22°C, the jerking completely disappears.

I'll reach out when I have data from VAG-COM. Thanks in the meantime!

short addition:

I just completed a thorough test drive with an outside temperature of 27°C, using the Climatronic system at its highest ventilation setting and the 'Lo' mode.
Apparently, 27°C is 'not enough,' as the shaking observed in previous attempts did not occur this time. Even with the use of 'auxiliary devices' such as the rear window heater and full illumination, the on-board voltage remained at 13.7V according to the Vag Com diagnostic tool, and the alternator load never exceeded 80%.
Can I therefore rule out possible causes of undervoltage or excessive compressor current?
Klimatronic seems to be diagnosable, and the following error message was found:
'1 error found:
01274 - Actuator for pressure relief valve (V71).
37-00 - defective.

Besides the rattling when the AC is running at full power and at extreme temperatures, I haven't really experienced any problems with the air conditioning system, except that I sometimes think it could cool a bit more...

Thank you for any advice.

Määtes wrote:

Except for some rattling when the cooling is at full power and at extreme temperatures, I haven't really had any problems with the air conditioning, other than sometimes I think it could cool down a bit more...

In a 5-year-old vehicle, you likely have at most half of the coolant (and oil!!!) remaining in the system. This reduces the cooling efficiency. I would generally recommend a complete refill (around 60,- € at a climate service center). While this might not directly address your original problem, it's worth trying.
Even if the air conditioning system is not adequately supplied with the added oil, it will suffer. Therefore, it's advisable to have this maintenance performed approximately every 3 years.

Best regards,
Uwe

@Friends:

Yes, I would rule out undervoltage as a cause.

The issue with the recirculation flap usually won't significantly affect the cooling performance; it just means you're driving with a higher or lower proportion of recirculated air. However, it can cause the windows to fog up even with the air conditioning running, so you should definitely investigate that. It looks like you might need a new actuator motor.

Before that, I would like to perform another actuator test on the control panel of the CT.

"However, that stuttering won't get you any closer to a solution. In your case, I would take the car for a drive in hot weather with a diagnostic tool and wait for the phenomenon to occur. Keep an eye on the coolant temperature. It might be a compressor shut-off, which my older model also did frequently in traffic jams, even though the coolant temperature, as indicated on the combination instrument, was 90 degrees. You can pretty much ignore that display; it's artificially set to 90 degrees and has very little informative value."

Refilling the refrigerant is definitely a good idea; in my case, 75% of it had leaked out after 4 years.

The issue with the recirculation flap usually won't significantly affect the cooling performance; it simply means you're operating with a higher or lower proportion of recirculated air.


That's not entirely correct. The recirculation flap controls the airflow at higher speeds. The faster the speed, the more air would be forced into the car, which would reduce the cooling performance because the Climatronic system is not designed for that level of airflow. Therefore, this flap closes as the speed increases.
In addition, it closes automatically when the interior is hot, which helps it to cool down faster. The condensation only occurs during the colder months.

Thank you for the helpful tips!

Right now, I'm 'unfortunately' unable to reproduce the stuttering (for a proper test), but I'll keep an eye on it when it gets hot again. In any case, I'm planning to have the system refilled soon; I've been considering it, but it doesn't quite seem related to the stuttering...

I can imagine that the ventilation flap is related to the recirculation system; I've had the problem several times in the winter where I couldn't almost completely clear the windshield, even in automatic mode.

Regards,
Martin.

Määtes wrote:

...had the problem several times in the winter that I could hardly clear the windshield, even in auto mode.

The compressor stops working at temperatures below approximately +3 degrees Celsius. If you were driving with the air conditioning on beforehand, condensed water may enter the airflow, causing the windows to fog up. Even when the system is operating at reduced power, it still dehumidifies, albeit to a lesser extent, but only at significantly above-freezing temperatures.
Since the problem only occurs when the compressor is running, I suspect the issue lies there. It's possible that the compressor is constantly being switched on and off via the magnetic clutch. This often happens when there's too much refrigerant. However, you mentioned you have too little, which doesn't quite align with that.
If the error occurs, you can try to listen for a clicking sound from the solenoid valve. I think that will help you pinpoint the problem.

Best regards,
Uwe

@Uwe!

Yes, I think I can hear the solenoid valve clicking. The last time the engine misfired, I stopped the car, turned the air conditioning up to max, and turned on the rear window defroster. Then I took a closer look at the engine:
- Turn on both fans.
- At the specified shaking frequency, a loud clicking sound was heard from the front left side of the air conditioning compressor, and each click caused the entire engine block to shake.

I assume that the compressor was switched on and off at short intervals, which then led to a build-up of pressure.
I should be able to see that with VAG Com, because I can check the clutch's on/off status there.
I suspect there's a thermal issue involved, because as I mentioned, there are no problems at the current temperature of 28°C. The most likely cause is probably a coolant shortage, which would lead to increased heating.

It might take some time before I find the opportunity to delve deeper into the matter, as I currently still live in Paris and am in the process of looking for an apartment in Bordeaux. Since cars in France are purely a means of transportation, and the necessary respect when parking is often lacking, I am currently just happy when I find my car in a reasonably undamaged condition...

Thank you for the tips, I will let you know if I have anything more specific to report.

@Uwe

In a 5-year-old vehicle, you will have at most half of the coolant (and oil!!!) remaining in the system.

The technician from the air conditioning company told me something different. He said that the refrigerant evaporates and leaves, while the oil remains in the system. I can't say how true that is. In my case, the air conditioning system was evacuated and no oil was added, for that very reason. The system is working again, although I also think it could cool better. However, the technician also said that the system is no longer good because it reaches a temperature that is 5° higher than usual.

Best regards, WarLord.

Hi!

I'm not entirely sure myself, but I got this information from a colleague who works in the field. He says that the performance of the air conditioner is proportional to the amount of refrigerant it contains, so 63% refrigerant fill means 63% cooling capacity.

During the evacuation process, which essentially means draining all the coolant until there's absolutely none left, there shouldn't be any oil remaining either, otherwise you wouldn't need to refill it. I believe that the coolant loss also simultaneously causes oil loss. My AC technician also reported frequent failures due to low coolant levels, which suggests a problem with the oil supply.

Our service costs only 60 euros. Afterwards, you have a well-cooling system and the certainty that everything is in order.

Best regards,
Uwe

That's the thing. My HVAC technician, who only deals with climate control systems, said that the oil remains in the circuit and only the refrigerant evaporates, and even during evacuation, the oil would remain in the circuit.

Best regards, WarLord.

Uwe wrote:

During the evacuation, which is nothing more than draining the coolant until it's absolutely zero, there's no oil left afterwards, otherwise you wouldn't need to refill any.

And how do you explain this?

Best regards,
Uwe