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Old 07-03-2015, 12:04 AM   #1
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Default Need help on iac2 fan control

(ms2 extra v3)I am having some diffuclty using iac2 wire to run my fan. I can not get iac2 to program off and on. I have the jumper from s12c to js9. is there something else i need to mod the board for? maybe jump iac2 to js2?
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Old 07-03-2015, 09:08 AM   #2
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nothing goes to iac2 by default on a v3.0 mainboard -- it's just a hole on the db37 connector.

You have to do something in order to make a wire on IAC2 to perform a function.

that means a specific circuit to drive a specific function, needs to be connected to the IAC2 hole on the board, then that circuit that performs a function has to connect to the CPU.

The so the CPU says: hey fans come on, and sends a signal to the circuit, which sends the signal to the iac2 wire, which controls whatever is on the other end of it (in the case the fan relay).
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Old 07-05-2015, 11:07 AM   #3
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so i can't just do this with the iac2 wire? i have to build a little transistor circuit?

IAC Spare Ports

The following IAC outputs are capable of driving over 0.5 Amp directly, sufficient for most automotive relays. You can connect to them using the IAC pins on the DB37 (25, 27, 29, and 31). Also, note that IAC1A and IAC1B are inverted relative to each other, as are IAC2A and IAC2B.

IAC1 - PT6,
IAC2 - PT7.
The IAC pins come out at:

(1A)JS0 to IAC1A - DB37 pin 25,
(1B)JS0 to IAC1B - DB37 pin 27,
(2A)JS0 to IAC2A - DB37 pin 29,
(2B)JS0 to IAC2B - DB37 pin 31,
Be sure to install a jumper from the hole marked S12C to the hole marked JS9 (+12C).
NOTE: PT6 (IAC1) and PT7 (IAC2) setting are reversed in MegaTune 2.25 (as of May 15, 2006), so PT6 in MegaTune actually affects IAC2, and vice versa. This will be corrected, so later versions of MegaTune may be correct. As always, you should TEST your configuration before using it in a car.

Also, after setting the second condition's value, you may have to hit the 'Tab' key to get the value to register.

The two spare port "T" pins (PT6 and PT7) are normally used to drive the stepper motor chip (IAC1,2). When you set pin PT6 high, it will make 1 of the 4 stepper output pins high and the other low, and no effect on the last two - which are controlled in the same way by pin PT7. So, by picking 2 of the 4 IAC outputs, you have two 12V spare pins that will directly drive about 0.5 Amps with no transistor needed. This is more than enough to drive a relay directly. If you are going to use port PT6 or PT7 as spares (IAC1,2), be sure not to set the idle control algorithm to any of the stepper control options (''IAC Stepper Moving Only', 'IAC Stepper Always On', or '15 Minute IAC'). This will keep the the stepper chip 'always enabled' and not turn it on and off, which would prevent the port from working as intended.
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