ECU pin 6 odd behaviour.

[k.alle]

Hi,

Not sure if this belongs in HVAC or Aftermarket ECU section, sorry if its wrong.

So I have hooked up pin 6 to my MaxxECU so that it knows when AC is running.
Initially when it is hot in the cabin and the AC is going full beans it works as expected.

Strangely when it starts to come down in temp and fanspeed decreases to maintain lets say 21 deg C the AC ON signal is lost through pin 6.
I really cant understand why because when looking in channel 52 on the climate control the compressor is still activated in this scenario.
I also had a look at channel 20 which shows the voltage output to compressor and it is steady in at 12v, and the magnetic clutch is engaged.

So what is happening here that is confusing the ECU to think that compressor is switched off when reaching desired temperatur in the cabin?
Is there some resistor or other black magic electricity that needs to be added to the pin 6?
This of course wouldnt bother me if the engine did not almost stall when coming to idle.

This is how pin 6 is configured in MaxxECU.
Pin 6 -> GPO7 (converted to DIN3)
DIN3 -> AC request/idle up

[jonn48]

Hi,

Not sure if this belongs in HVAC or Aftermarket ECU section, sorry if its wrong.

So I have hooked up pin 6 to my MaxxECU so that it knows when AC is running.
Initially when it is hot in the cabin and the AC is going full beans it works as expected.

Strangely when it starts to come down in temp and fanspeed decreases to maintain lets say 21 deg C the AC ON signal is lost through pin 6.
I really cant understand why because when looking in channel 52 on the climate control the compressor is still activated in this scenario.
I also had a look at channel 20 which shows the voltage output to compressor and it is steady in at 12v, and the magnetic clutch is engaged.

So what is happening here that is confusing the ECU to think that compressor is switched off when reaching desired temperatur in the cabin?
Is there some resistor or other black magic electricity that needs to be added to the pin 6?
This of course wouldnt bother me if the engine did not almost stall when coming to idle.

This is how pin 6 is configured in MaxxECU.
Pin 6 -> GPO7 (converted to DIN3)
DIN3 -> AC request/idle up

Try using pin 41. Pin 6 seems to be used to turn off the AC compressor when a large throttle is open.

[k.alle]

I am using Pin 41 for turning off the AC on large throttle.
Which is working as intended.
If I look at CH52 on the climate control during WOT I can see that it is turning off the compressor with "compressor off requested by ECU" code.

I'm not sure that would work on Pin 6.

[EDIT]
Oops, I might just be an idiot.

Just read this on S2Central:

06	Air conditioning compressor control. Normally an input in conjuction with pin 41 , but can also be used to turn off A/C compressor when maximum engine power is required

41	Air conditioning status - informs the ECU if A/C is ON or OFF

It seems I have them confused as you said jonn48.
Weird that it works to send signal on Pin 41 to turn off compressor as well.

[jonn48]

I am using Pin 41 for turning off the AC on large throttle.
Which is working as intended.
If I look at CH52 on the climate control during WOT I can see that it is turning off the compressor with "compressor off requested by ECU" code.

I'm not sure that would work on Pin 6.

[EDIT]
Oops, I might just be an idiot.

Just read this on S2Central:

06	Air conditioning compressor control. Normally an input in conjuction with pin 41 , but can also be used to turn off A/C compressor when maximum engine power is required

41	Air conditioning status - informs the ECU if A/C is ON or OFF

It seems I have them confused as you said jonn48.
Weird that it works to send signal on Pin 41 to turn off compressor as well.

https://forums.quattroworld.com/s4s6/msgs/309099.phtml

Here is a description of pin 6 and 41. Although there is one strange point described in the topic on m.2.3.2. There was no increase in speed when the air conditioner was turned on, although this algorithm was written in the firmware code. I tried to write the original rs2 firmware in ECU, but it didn’t work on it either. This was tested on s6 AAN. I had suggestions that the rs2 uses pin 6 for this, but I never tried it. What is your car?

[k.alle]

Thank you, that is interesting.
So it could have been implemented differently between S2/RS2/S4/S6?
My car is ABY hooked up with MaxxECU.
WIring loom is ABY.

[jonn48]

That was my guess. On all circuits that I found, pin 41 was used.

[k.alle]

Soo....
It turns out that I indeed had connected Pin 41 to DIN3 on my MaxxECU.
The thread title and most of the thread is thereby misleading, sorry.

Since that checked out I tried to move it to DIN5 instead and try the signal with "5V pullup enabled".
Unfortunately its still behaving in the same way, loosing the compressor on signal when cabin temp is "reached".
Switchnig between active low and high just inverts the problem.

I have tapped in to Pin 41 on a connector under the steering wheel / kick panel.
Should I take the signal from the compressor relay instead?
Any ideas?

[jonn48]

Soo....
It turns out that I indeed had connected Pin 41 to DIN3 on my MaxxECU.
The thread title and most of the thread is thereby misleading, sorry.

Since that checked out I tried to move it to DIN5 instead and try the signal with "5V pullup enabled".
Unfortunately its still behaving in the same way, loosing the compressor on signal when cabin temp is "reached".
Switchnig between active low and high just inverts the problem.

I have tapped in to Pin 41 on a connector under the steering wheel / kick panel.
Should I take the signal from the compressor relay instead?
Any ideas?

Yes, the climate control behaves the same on the Ecu runoff, when it is necessary to cool or heat the interior, there is a signal to increase the speed. When you just need to maintain the temperature, there is no signal. In your case, you can simply connect to the + power of the compressor clutch.

[k.alle]

Thanks for that info jonn48, that would indeed explain the issue.
Since the load from the compressor is still there even though the cabin temp has been reached the engine almost stalls when coming down on idle.