Tim Murphy

As Vlocity mentioned, the fans typically are shipped as a puller style fan. The front AUX fan most lilely needs to have the fan blade pulled off and reversed (don't just reverse the wires).

Did you wire all four 8" fans together on the primary circuit? This does work.

Btw Vlocity, that is a sweet looking heat exchanger you have there!

Bill Ball

Yep, figured that out eventually.

We decided to wire the auxiliary pusher as primary and the muffins as seconday, as Kevin did, because the aux fan blows right over the SC. We will see how it cools tomorrow after we finish a few more tasks. At this point they all seem to come on together anyway.

Also, Kevin commented that the muffins run slow when all ganged in parallel. Would there be a worthwile advantage to giving each muffin or muffin pair direct power controlled by the fan circuit via a relay?

Bill Ball

No, this was required to get all the muffins spinning counter-clockwise (pulling) viewed from the behind. Seems nuts.

the flyin' scotsman

The fans are DC (direct current) so they'll run either way depending on how they're wired with no worries.

aggravation

Seems odd to me that a separate power supply wire to each motor would make any difference unless the singular power supply wire is too light of a gauge to carry the cumulative amp draw of all the motors. Parallel is parallel...whether you run each motors lead all the way to the battery separately or bring the battery's power to a forward location via a single heavy wire and then branch each motor lead from there as long as they leave the power source in parallel they should have full potential regardless of them sharing the connection point.

Now, if you wire them in series then you will see a power loss...

But then again I'm an HVAC/R mechanic not an auto mechanic and I didn't stay in a Holiday Inn Express last night so I could be ignorant of something here

Bill Ball

Perhaps one reason to wire them directly is that the stock fan control system through 91 never supplies full voltage even on full; rather it cycles the voltage. In 92 this was changed...

From 92 Service Info Booklet:
"Radiator Fan Control Unit
Improvements were made to the control unit of both radiator
fans. If full fan output is required, the radiator fans receive full
system voltage. On older control units, even in the “final stage”
system voltage was supplied to the fan motors only in a cyclic
sequence."

It seems with the potenial high heat load it might be more effective to skip all the complicated staging Porsche built into the system and go full on.

If there is no slowdown from ganging the fans then all we need to do is provide all of them a single direct power supply, to get full voltage, controlled via a relay with the fan circuit. However, the gage of the wire to the plugs in the fan system is pretty small, so I wouldn't be surprised if the wattage of the supply was limited somehow by the controller. I understand it limits voltage and that alone could be an issue.

aggravation

Ahh, good point, I was assuming the fans either received voltage or didn't..on or off based on the temp switch, I didn't realize the fan controls were that sophisticated. It sounds like you're right, a redesign is in order to make sure the new fans get the power they need when the temps rise.

Is there any down side to having the fans run anytime the engine is running above a minimum temp? Seems like the thermostat bypassing the radiator is all the variable temp control we really need anyway. I'm out of my league now, I'll just stand back and learn....

Bill Ball

That's how most cars work. Reading the description of the 928 fan control operation would give most people a very large headache.