Originally posted by Scott4DMny
... The ecm has a High and a Low fan setting. I believe that when it reaches a certain temperature (different settings with different chips, but I will give you an example)
Lets say my ecm is set at low fan for 175 degrees to come on.
The high is set to come on at around 210 degrees I believe.
so basically, the center part of my 3-way switch is called "chip" in which the fan is controlled by the ecm.
The upper part of the switch is for high, and the bottom for low. Now this low and high is for manual control, meaning if I want high fan on all the time, I hit the high button section, if I want low, I hit the low button. Otherwise, I put it to chip to let the computer control it. ...
Scott,
Years ago I vaguely recall Kenne-Bell has some wiring kit that would let you do basically what you describe.
Here's my take on it:
1) why would one need a manual, "always on", low speed fan setting? The ECM chip will always TRY to control the low speed to maintain the temperature programmed in the chip. May not always make it with a stock fan.
2) standard relay setup in 86-87's is ECM control of fan at "low speed" only. With the stock fan, it's my understanding the temp could still rise to ~220F. With the Ramcgharger/Valeo fan, would low speed ever rise to ~220F?? I don't know.
One option is to wire the RC/Valeo fan to ALWAYS run high speed under ECM control. Then I have little doubt the ECM could ALWAYS control the temp to what's programmed in the chip. But I suspect the fan would be quite noisy if it was always toggling between "off" and "high" speeds.
The programmed temp varies by Chip mfr, but in Extender chip I think it's around 170-175F maximum.
3) if we let the Chip only operate the RC/Valeo fan at its low speed, then yes, I can see the benefit of manual high speed control to quickly cool the engine on a super hot day.
But I'd prefer the high speed operate off the stock high speed time-delay relay, so that fan eventually shuts off automatically after 10 minutes with ignition off (else you could forget the fan "on" and drain battery!).
I think this is what the old kenne Bell setup did. Equivalent function is achieved by having a manual switch that grounds the over-temp coolant switch in the intake manifold.
4) a connector on the Racetronix harness to manual activate a *timed* high speed fan might be nice but not essential.
5) I don't see the benefit, at all, of having a manual 'always on" low speed fan.
6) IMO, a jumper or similar to allow ECM control at either LOW or HIGH fan speed might be more useful. Cars in Nevada, Arizona, or the South might want the ECM to always control at high speed. In winter or cooler northern climates, ECM control at Low speed alone, might be adequate.
In all cases, the coolant over-temp swich would activate high speed fan at 220F.
7) IMO, the Racetronix harness "as is" , is perfectly fine. There's many different design decisions one can make, all perfectly rational and sensible. There's not necesarily a "wrong" or "right" way to design the function. A lot of time and money could be spent redesigning the harness's function. It would be "different", but not necessarily better or worse.
In the engineering world there's a phrase for this, called "feature creep", "scope increase", or similar. ie, Keep adding features at ever increasing cost and schedule delay, to meet every conceivable need.
I've seen many a project get derailed due to undisciplined "scope increase". This is not always the optimum or most practical approach to product design.