 | Home > Td5 > ECU control of Air Conditioning system |
 
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| TexasRover Member Since: 24 Nov 2022 Location: Paris Posts: 800   
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I don't think there is any magic in that 'AC computer'. There are inputs (standard AC stuff and temperature) then there is the user input (little bit cold or barely cold). The 'AC computer' creates an AC clutch and AC fan demand based in ac pressures and evaporator core temperature, which is then routed to the Td5 ECU purely to give the ECU a bit more info to play with (cut AC comp load at high power demand, switch on AC fan for additional cooling if required etc).
Really it is a glorified thermostat. The interior fan speed is entirely separate from what i can see. |
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25th Jul 2023 3:30pm |
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| JohnDEF Member Since: 25 Jul 2023 Location: Chesham Posts: 4  
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hi TexasRover
I agree that there isn't any magic or any advanced sophistication in the system - there's only two demand signals - compressor and fan, and two output signals to switch each on/off independently. My question really relates to how the two input channels work. These are driven by user controlled switches, but the ECU seems to prevent the user command (via the switches) being executed until it determines that the engine conditions are right (such as engine is running, revs above a certain limit etc) - all kind of obvious stuff, although I've never seen documented ... But my real question is - or do I understand it correctly ... the ECU seems to hold the inputs at 12v (thus preventing the circuit from completing). So, my expectation is that the ECU will drop the inputs to ground once it decides the engine conditions are appropriate. The bit I don't know - does the ECU ground those two wires. If no, what does ... |
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25th Jul 2023 4:27pm |
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| NickMc Member Since: 01 Oct 2014 Location: Norn Iron Posts: 1572  
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 Click image to enlarge |
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25th Jul 2023 4:49pm |
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| TexasRover Member Since: 24 Nov 2022 Location: Paris Posts: 800
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The ECU signal drives ordinary 12v relays, so yes looking at the circuit diagram the ECU pulls to ground to energise the relay
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25th Jul 2023 5:08pm |
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| JohnDEF Member Since: 25 Jul 2023 Location: Chesham Posts: 4
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hi NickMc
that's from the manual and describes how the demand signal works from the AC side, but it doesn't describe what the ECU does on the demand inputs. I've measured 12v at IGN on and with the engine running on the ECU side of the input wires. If the HEVAC sets a demand signal, presumably +12v, then nothing happens. ECU has the input pin at 12v. So, I'm assuming the ECU grounds the inputs and at that point it can 'see' the demand signal. But that's my assumption. Can't see anything in the manual that actually describes how the ECU logic response on AC demand inputs. It might well be the case that this isn't documented by LR ... |
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25th Jul 2023 5:09pm |
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| NickMc Member Since: 01 Oct 2014 Location: Norn Iron Posts: 1572
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Yes ECU normally will switch to ground
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25th Jul 2023 5:22pm |
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| JohnDEF Member Since: 25 Jul 2023 Location: Chesham Posts: 4
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All the above suggest that the ECU signals on these pins are high (+12v) for OFF and low (0v) for ON.
Does that sound consistent with other ECU signals? Maybe any Nanocom experts out there might be able to comment? |
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26th Jul 2023 5:57pm |
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| NickMc Member Since: 01 Oct 2014 Location: Norn Iron Posts: 1572
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I looked at my Autologic today and it doesn’t give much else in info, than what you already know, but Ive attached below
Click image to enlarge |
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26th Jul 2023 6:39pm |
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