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TDI Conversions Discussions on converting non TDIs into TDIS. More general items can be answered better in other sections. This is ideal for issues that don't have an overlap and are very special to swaping engines.

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Old September 16th, 2017, 19:11   #1
Motohead1
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Default AC Switch/ON 121 ecu pins?

Can anyone tell me what pin on a 2002 121 pin ecu (ALH) gets the "AC Switch" signal? I see on VCDS this one will actually raise the idle and I assume might do somthing to the timing and fuel maps.

I found the "Compressor ON" pin that does not raise idle or do anything that I can see but in the bently I dont see the "AC switch on" pin.
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Old September 17th, 2017, 19:13   #2
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For more context here is the wire diagram showing pin 121/34 is the "Compressor ON" trigger. Just need to find the pin that sets the "AC Switch on" command.


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Old September 25th, 2017, 20:30   #3
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Hey motorhead1 the sticky ALH PINOUT shows t10 orange 4 ws. As ac related, t10 orange 7 gn t121/29 ,t10 orange 9 gn/br ac related, t10 orange 8 bl/ro t121/34 I'm also interested in this.my ac works good in my swap but I like to hook this up to my coolant glow plugs relay to increase idle speed at cold start warm-up
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Old September 26th, 2017, 00:45   #4
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tdi self corrects idle to 903 rpm regardless of load ... it doesn't need an AC signal to achieve this ... stock vw tdi's do not "idle up" when you turn on the AC they simply maintain 903 rpm
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Old September 26th, 2017, 08:01   #5
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Quote:
Originally Posted by jimbote View Post
tdi self corrects idle to 903 rpm regardless of load ... it doesn't need an AC signal to achieve this ... stock vw tdi's do not "idle up" when you turn on the AC they simply maintain 903 rpm
Dude are you a VW engineer? Christ you're a wizard of knowledge with this stuff . I swear almost half of the notes in my notebook are from your posts.

Last edited by Tacoma_TDI; September 26th, 2017 at 08:03.
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Old September 26th, 2017, 18:45   #6
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Quote:
Originally Posted by tdihuntdawg View Post
Hey motorhead1 the sticky ALH PINOUT shows t10 orange 4 ws. As ac related, t10 orange 7 gn t121/29 ,t10 orange 9 gn/br ac related, t10 orange 8 bl/ro t121/34 I'm also interested in this.my ac works good in my swap but I like to hook this up to my coolant glow plugs relay to increase idle speed at cold start warm-up
Ahh pin 121/29 that might be it thanks!

Quote:
Originally Posted by jimbote View Post
tdi self corrects idle to 903 rpm regardless of load ... it doesn't need an AC signal to achieve this ... stock vw tdi's do not "idle up" when you turn on the AC they simply maintain 903 rpm
Yes it does self correct to 903 rpm but from my understanding if the ECU knows the AC is ON the timing and fuel maps can be slightly affected if parameter limits start to be reached. Its probably not much but I have been chasing a overboost issue and it seems to be more apparent when the AC is on. I just want to rule it out before I ask the tuner to look at it again.
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Old September 27th, 2017, 01:42   #7
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Quote:
Originally Posted by Motohead1 View Post
Ahh pin 121/29 that might be it thanks!



Yes it does self correct to 903 rpm but from my understanding if the ECU knows the AC is ON the timing and fuel maps can be slightly affected if parameter limits start to be reached. Its probably not much but I have been chasing a overboost issue and it seems to be more apparent when the AC is on. I just want to rule it out before I ask the tuner to look at it again.
if you have overboost that's a completely unrelated issue to running the AC... if it does indeed effect timing/fueling it's purely from an emissions standpoint and would not cause overboost ... it's just another load on the engine, like an variable alternator loads or power steering loads, that the ecm automatically compensates for ...
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Old September 27th, 2017, 02:07   #8
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can you post logs of your boost and N75 ? maybe we can help figure the overboost issue
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Old September 27th, 2017, 18:50   #9
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Ill log it in the morning trip to work but I changed the N75 a few weeks ago even though mine tested good and didnt look weird on logs from what I could tell.
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Old October 3rd, 2017, 18:41   #10
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Confirmed pin 29 needs also hooked up. Also tune was tweaked and no more overboost so far. Basicly added a little more boost down low. burns a little cleaner also now.
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