'165 switching both fans from the ECM?

[David C. Allen]

The Coolant temp (A/D Ch 4) input on ECM Pin C10, controls output ECM Pin 
C1, which controls the Fan Relay.

The A/C Pressure input on ECM Pin D11,  Also controls output ECM Pin C1, 
which controls the Fan Relay.

you only have the one A/D Ch 4 (input Pin C10) that is doing the resistance 
to temperature conversion in the ECU.

So it looks like you would have to write the routine that looked at  A/D Ch 
4 and then controls output ECM Pin C11

Adding the second fan control relay to ECM Pin C11 and then controlling 
your second Fan.

You could also do a 2 speed single fan with low speed/(on off) controlled 
via output ECM Pin C1, and high fan controlled by ECM Pin C11

Maybe a better solution would be to Pulse Width Modulate output ECM Pin C1 
and drive the fan via a control circuit instead of using a relay. Now you 
have a continuously variable cooling fan that runs at a speed based on 
engine temp or A/C pressure.


David










At 04:38 PM 05/27/2000 -0400, you wrote:
>At 11:55 PM 5/26/00 -0400, you wrote:
> >Somehow, I just knew you didn't want to do things the easy way. : )
> >Well, I'm looking at the ecm pinouts for an 89 F car, and it appears
> >that the ecm controls 2 fans.  The vettes are similar, but I won't
> >swear that the wiring is the same.  Pin C1 is for the primary fan, pin
> >D11 controls the secondary fan.  D11 is wired in parallel with a temp
> >switch in the cylinder head.
>
>Looks like D11 is actually sampling the AC pressure switch for continuity
>to ground.  This is the case on '88, '89 Vette, and '86 F-body pinouts in
>my Helms and the diy-efi incoming directory.  It uses this input to
>determine whether the AC compressor is running, setting the flag for all
>the "AC pressure high" options.  Looking at the Helms manual, D11 shows up
>as strictly an input path.
>
>This creates a new mystery...how do BUAs control the aux fan?  There's
>logic for it in the .bin but I'm not finding an ECM pin where they drive it.
>
>Hmmm....
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