Air conditioning occasionally blows warm air, Passat B7, year 2011

Hello fellow DIY enthusiasts,
My name is Lukas, unfortunately I'm already 30 years old, and I drive a Passat Variant, model year 2011 .

I'm currently on vacation in Italy, and I'm having a problem with my air conditioner. My wife is already complaining because I'm constantly on my phone, trying to figure out how the air conditioner works. The topic is really quite complex...
But now, let's get to the problem...

In 2015, the climate control compressor was defective. The compressor, dryer, and expansion valve were replaced. Climate-controlled and refilled.

Now, the air conditioner cools, but after a while, it simply starts blowing lukewarm air. This lasts for about 2-5 minutes. Then, the air conditioner automatically starts blowing cold air again. I believe I can interrupt this process by turning off the AC for about 10 seconds and then turning it back on.

Furthermore, I've noticed that when I'm driving on the highway, the air conditioning works without any problems starting at around 60 km/h. As soon as there's a traffic jam on the highway and lower speeds are possible, the air conditioning starts blowing lukewarm air again.

If the error occurs, I once saw that the air conditioning fan was not running. Even though the car had warmed up and it was 25 degrees Celsius outside...

The error also occurs in the "Low" position.

That's why I went to the workshop that replaced the compressor in 2015. They only found one error there... Air quality sensor malfunction.
"This unit has been replaced. The refrigerant level has been checked and the system has been refilled. Unfortunately, the issue could not be resolved before the vacation. The workshop is unfortunately unsure of the cause... Now I'm no longer willing to pay any more money for troubleshooting. A VCDS diagnostic tool has been ordered. Unfortunately." I'm still on vacation for another week.

My question to you is: Does anyone here know about this issue? Does anyone have any ideas?
Is it difficult to read the sensor data from a VCDS and compare it to target values?

I've already read so much! Unfortunately, I can't find a specific point where I can start. Despite this, I've made some notes of points I want to check using a VCDS diagnostic tool when I get home.

Defective ice protection switch?

Is the expansion valve clogged?

Is the climate control pressure switch defective?

The temperature sensor on the pre-evaporator may have a different temperature reading. Image error: Pre-evaporator freezing, climate control system failure.

Vaporizer temperature sensor error?

The climate control fan is not switching to the second speed setting.


Unfortunately, I have no idea how to address these points or whether they even apply to my vehicle... (Does the air conditioning fan even have two speeds?)

Thank you in advance.

Hi,

When the air conditioning is turned on and the vehicle is stationary, at least one radiator fan must be running.

In your case, the climate control system isn't removing the waste heat, and the pressure builds up until it triggers a safety shutdown due to overpressure.
If there is airflow, it provides sufficient heat dissipation from the air conditioning condenser.

I'm assuming that your air conditioner isn't overcharged.

Thank you for the response.

During the last inspection 7 days ago, it was discovered that 100 grams were missing. The error was already there before that.

Are you referring to the large fan or the small one that's located directly in front of the compressor?
I noticed that the two fans are running in opposite directions.

Can I use VCDS to perform a log recording and check what the small A/C cooler fan is doing when the error occurs?

Does this even have two levels? Full load and fully loaded?
As I said, I don't have the VCDS yet; I just ordered it and need to get home first.

Thank you.

Basically, both fans serve the same purpose: to remove warm air. It doesn't matter whether the warm air comes from the engine or the air conditioning system. The fan control can be different. Usually, the larger fan has two speeds, while the smaller fan has only one. However, there are also combinations where the small fan has two speed settings.
That means:
Today, there is no fan that is only responsible for the air conditioning system. What is important is that the heat (regardless of its source) is removed. With the system stationary and the air conditioning turned on, it means that at least one fan speed must be running to dissipate the heat.


Yes, with VCDS, you can diagnose the function of the fans and also the status and deactivation conditions of the air conditioning system (provided the air conditioning system is original equipment).

Yes, the air conditioning is the original factory-installed equipment.

What makes me suspicious about the whole thing is that no other error is being registered. It's likely a faulty sensor. Deviation from the actual value, or something like that...

monsenseg wrote:

... What makes me suspicious about the whole thing is that no other error is being registered. It's likely a faulty sensor. Deviation from is value or something...

Is the fan broken, or just one of the fan speeds?
It can usually be checked very well using actuator diagnostics.

Okay, great. That's already something I can test. I didn't know there was something like that in the vcds.
Looking forward to the vcds. I just hope it's not too complicated...

Definitely a case for VCDS. Check the error memory of the climate control system, as it logs errors in the control unit. You can also test the radiator and air conditioning fans using VCDS. When the air conditioning is on, they should always be running on a low setting, in my opinion.
The reasons for deactivating the climate compressor are also displayed in the corresponding measurement block.

Best regards, Rainer.

The error memory was read, and it only showed the error "Air quality sensor defective," which will be replaced. After that, there were no more incorrect entries.

What happens when there are no more errors? My concern is that when I take my car to the workshop, they might, in the worst-case scenario, try to rip me off .

Quote:

The reasons for shutting down the climate compressor are also displayed in the corresponding measurement block.

I don't know anything about VCDS. And if the workshop tells me that there was only one error, I assume that's correct and that everything else was also checked.

I probably still have the idea that you just plug in a VCDS and all the errors are displayed directly. I didn't know that you had to look for errors in "measurement blocks."

I still need to learn how to interpret measurement data or identify potential errors.

Error = Error memory.
Shutdown conditions = measurement block.

It's not generally a problem if the compressor is turned off.

VCDS will not cause any problems by connecting to a vehicle. It's simply an incredibly useful tool for understanding vehicle functions (or, in your case, anomalies).

Without knowing the shutdown conditions, if any exist, remote diagnosis is not possible.

You can check if the expansion valve is frosted. In this case, the interior will not be cooled.

I'm still on vacation in Italy... Vcds is already back home. My wife wants to stay there for another week.

How can I check if the expansion valve is frozen? Just put your hand on it?

Yes, but be careful. You don't want your skin to stick to it. The best approach is to wait for the moment when the interior is no longer being cooled.

vag-driver wrote:

Yes - but be careful. Don't let it stick to your skin. The best approach is to wait for the moment when the interior is not being cooled.

Put on a glove, or at least place a cloth in between. Direct skin contact should be avoided.