Idle Speed with AC On: Troubleshooting & Tips

Hello.

It is widely stated that the engine idle speed should increase when the air conditioning is turned on. Or does this only refer to maintaining a certain speed? Mine remains at 945 RPM, regardless of whether the AC is on or off .
Is that okay?

Hi,

When you turn on the air conditioning (if it was originally installed), the control unit (ECU) is notified, and the engine speed is slightly increased to ultimately return to its original value.
My (retrofit) air conditioning system doesn't have that feature, and as a result, the engine struggles quite a bit even when idling!

By the way, the original KIMA system can also be deactivated by the TCU (Transmission Control Unit) under certain conditions: during kickdown, within 6 seconds after engine start, and when the engine temperature reaches critical levels.

Hi,

That's exactly how it is.
When the air conditioning compressor is activated via the magnetic clutch, the engine speed drops slightly, even with the original KA system.

I have a 'free rider question' (and don't want to start a separate thread for it):
Lately, I've been reading repeatedly that the refrigerant should be replaced after a few years because it gradually degrades over time, and the compressor could fail.
Now I've noticed (after 7 years without any maintenance), that the radiator fan is starting up more frequently when the air conditioning is on, which used to only happen during extreme heat or in 'hurricane' ventilation mode.
Does this indicate a low refrigerant level in the system?
Or does it simply indicate a declining performance of the cooling fins, which are supposed to get dirty over time?

Hi again!

Thank you for the quick responses!

I converted a gasoline automatic car into a TDI manual transmission car myself, therefore I can't really provide the solutions that a new car would have.

As soon as I press the button on my air conditioning system, the fan turns on. Regardless of the weather or location. So, turning on the AC means the fan is set to level 1.
Level two, depending on the heating and cooling requirements.

Perhaps this will help you?

Best regards.

Nic @ DeathAngel69

...in fact, fan speed level 1 is always running.
I wasn't entirely accurate:
The second stage is happening more and more frequently for me, which is causing me some concern.

Markus H. wrote:

Hi, That's exactly how it is. When the air conditioning compressor is activated via the magnetic clutch, the engine speed drops slightly, even with the original KA system. I have a "free rider question" (and don't want to start a separate thread for it): Lately, I've been reading repeatedly that the refrigerant should be replaced after a few years because it gradually degrades over time, and the compressor could potentially fail. Now I've noticed (after 7 years without any maintenance) that the radiator fan is starting up more frequently when the air conditioning is on, which used to only happen during extreme heat or in the most powerful ventilation mode. Does this indicate a low refrigerant level in the system? Or does it simply indicate a declining performance of the cooler fins - which are supposed to get dirty over time, right?

Yes, the information is correct, and your assumption about it is also correct.
For retrofitted air conditioning systems (especially those with rubber hoses, which can be even more extreme!).