AC Malfunction: Causes and Solutions

Hello everyone!

Summer is here, and the climate analysis has already begun!
"I've had the feeling for the past few days that the climate control system is working very hard. So, I created a longer log file to investigate. What's noticeable is that..."

1. The pressure seems to be within the acceptable range. It's approximately 9 bar without the engine running, and about 14 bar with the engine running.
1a. Compressor torque between 11 and 18 Nm.
2. Outside temperature: approximately 31 degrees.
3. Evaporator temperature: minimum 5.5°C after 5 minutes in automatic climate control mode.
4. Between approximately 336 seconds and 511 seconds, I manually set the fan speed to the maximum.
5. bei 814sec. hatte ich Luft auf Füsse gerichtet, um den Temperaturfühler Verdampfer mit denen an den Austrittsdüsen Fußraum zu vergleichen. SchThat sounds plausible.

Remarkable:

Suddenly, the compressor control signal drops to 0. Simultaneously, the torque drops to 0, while the pressure only decreases slightly.

EDIT: Vehicle details from signature. So, it's an A3 Sportback 8PA, engine code CFGB (125kW CR), manual transmission, and automatic climate control.

Question:
Where are these glitches coming from??? There are no memory errors!

The raw log file and some vehicle data would be helpful.

Hello Auto Service,

I've added it above. Thank you!

Have you checked the interior temperature sensors for any anomalies?

No. Not yet. Good point! As far as I know, there's only one...? Directly in the climate control system...?
What I haven't found yet in the measurement data blocks is the desired temperature, which I set on the climate control system.

Here's another question: Can I actually infer the correct filling level from the torque? As far as I know, this isn't really possible with HD (high-definition) data...

Quote:

Can I actually infer the correct filling level from the torque?

Good question. I think that, if at all, it would only be an estimate/guess, or the software would be so clever as to factor in the vehicle's wear and tear, which would be a utopia .

The actual fill level can only be determined by measuring the amount of coolant that has been pumped out.

Under what conditions was the log recorded?
While driving or when stationary?
If the first condition is met, the next question is what the motor load was at that time.
If you're going to do it, pay attention to the coolant temperature... especially the temperature of the low-level coolant.
The engine management system plays a significant role in regulating the climate control today. Especially with extreme outside temperatures, the engine can overheat and shut down the air conditioning system (even temporarily), particularly with the 125kW engine.


On Thursday, I was driving my motorhome, which was pulling a trailer, up the incline behind the Werrabrücke bridge on the A7 motorway heading south. At 8% incline with a trailer weighing almost 3 tons, that practically meant full throttle. Even shortly before reaching the incline, I could already feel warm air coming from the ventilation. The MSTG (presumably a system controlling certain functions) simply turned off the air conditioning. It wasn't until we started going downhill again that the compressor was reactivated, and noticeably cooler air flowed into the interior.
A completely normal process.

With your current setup, the high dynamic range (HDR) is still well within a normal range and far from reaching its performance limits.
According to Wie Autoservice, the refrigerant charge can only be accurately determined by weighing, for example, using a climate control service device. The pressure, especially the high pressure, varies significantly depending on the outside temperature, the fan that removes heat from the condenser, and the process of converting the refrigerant from a gaseous to a liquid state.
ND: Should be 1.9-2.2 bar, which translates to 1.9 bar at 0° and 2.2 bar at 3°. After the expansion valve, the air temperature is slightly higher, ranging from 2-9° depending on the blower level and intake temperature. If the evaporator is too cold, the compressor shuts off – this is a frost protection feature. It also shuts off under high motor load or high coolant/refrigerant temperatures.
In my Toledo ARL, which weighs 1500kg with the camper conversion, the air conditioning shuts off when going uphill at a mid-mountain elevation and with the accelerator fully pressed, due to the high temperature of the engine coolant, just like with Bertil!

Similarly, excessive pressure on the high-pressure side (approximately 30-35 bar), a faulty fan (stage 1/2), and very high outdoor temperatures (exceeding 40-45°C, which is beyond the design specifications for Europe; countries in the Arab region typically use more powerful fans or larger condensers designed for up to 55°C) can cause issues. Furthermore, significant contamination between the condenser and the cooling unit can occur, which is unfortunately only visible after removing the cooling unit or condenser.

Hello everyone!

Thank you for your active participation. In the meantime, I've made some progress.

You are indeed correct. The engine misfires are caused by the engine management system. While the misfires in this case don't have a thermal origin (the error log was generated while the car was stationary or during city driving), the air conditioning system absolutely and consistently shuts off under the following conditions:

1. Start the engine with a normal/low RPM and low load. Even if the engine doesn't jerk or make any unusual noises...
2. When the compressor is operating at its maximum output and you are approaching a traffic light, disengaging the clutch (presumably to maintain idle stability).
3. As soon as full load is desired (but only temporarily).

It seems that the system is running at its performance limit, possibly due to the current outdoor temperatures and potentially a less effective refrigerant charge after 3 years. I'll have it refilled next year before the summer.

If you have any other ideas, I'd love to hear them. I find the whole climate regulation topic very interesting.
What's still unclear to me is how the interior temperature is being measured. There's a sensor with a fan built into the control unit itself. According to the specifications, there should also be a passenger sensor and a driver sensor. Where are these supposed to be located in the A3?

EDIT: Done!

Block 21 - Field 2 Temperature (Actual) - The driver (G344) is NOT responsible for controlling the air conditioning; the seat heater sensor is. The same applies to the passenger sensor G345.

@Rainer: Perhaps it would be a good idea to declare this in more detail?


Regards,
Dirk.