First off reason or reasons : Ford has a list of priorities
Passanger being at or near the bottom of the list for
ramping up fan speed to keep the AC working at a stoplight
Also the PCM can't foresee the fact that you plan haling that
heavy load up a long climb (even with a fast recovery after).
Yes you can go to high idle but putting on the parking brake
and placing the truck in park has it's problems that is is if
the PCM will command the fan higher even with the added RPM
to offset the new LOAD requirement if any with the AC compressor
on.
So having a tool to look at things like a Labscope unit of in the VCM and VCM2
world a VMM. You can get them and they cost a LOT.

Now on to the question of the signal. The PCM uses a form of command
called current sink (see previous post for that link) it is quite simple
and easy to override (no fancy hardware) it can be done with a simple
switch or a more complex with a transistor circuit. I'll stay basic and simple
to not drive the greater reading public away with sleepiness. So to bd that
I will just say I have talked to and have done override control of the system
fan with a simple switch. The really nice part about a sink driven load is
if it is grounded after the load (in this case the system fan) it just becomes
stuck in an ON STATE and over cooling and giving a bit more LOAD to the
engine. The PCM will not see any added power draw because the fan gets it's
power from a fuse between it and the batteries and the clutch is self cooled
by the increased airflow and the builtin fins. The two things that will need to
be checked are what happens if power flow in on and engine (airflow) is off.
Will id self heat or not at this point. The other thing is MAX device operation
speed. We have not had a reported fan blow up that had been stuck on as of yet.

So I'll let you ponder this for a while with one last parting idea to ponder.
Have a look/search over at the .ORG because this topic has come up and been
talked about and Yes I was involved in it right before surgery and some other
craziness in life (And no I won't go into that).

Well time to let you ponder this.



Sean

 

Thanks Yahiko saves me trying to explain what you just said better.
I remember that discussion on the org. That was a good un. Nearly every forum I belong to has had that discussion from time to time.

 

If I had the cash on hand I would go about picking up a VMM and a real
VCM2 and the IDS subscription. Then doing all these tests would be so
much easier.

But like they say (If wishes were fishes we all would be fat).


Sean

 

Thank you for all your help! This helped me out with my decision and I might just try something once the summer heat hits again. Probably going to try a good pwm board running with an ssr to see if it'll work right after some testing. The boss just bought a new scan tool that seems to have some different info from the last. I'll write an update post if i can get it to work.
I love this site