Without to much modification or wire cutting how can I safely modify my S4 fans so one is always on and the second on with a switch.
Is the wiring similar to the interior lighting where 12 volts is constant and the ground is the switch?
Of course I’d like to keep the fuses in the mix and have the ability to go back to stock easily.
(Alan)

 

First thing you would need to do is bypass the PWM units. You would then need to fit a relay in each fan supply cable- one energised by a running contact of some kind and the other energised by a manual switch.
It should not be too difficult to realize but given the superior kit Porsche installed it would not be the smartest thing to do on these cars albeit I can understand the frustration if you have issues .
This has been done before and the Aussie outfit that make electric water pumps have some neat kit that helps facilitate such modification. Look up the Davies Craig website and you will find such kit quite reasonably priced

 

There is no means to do this with the stock configuration, there are no relays switching the fans - they are both driven by a common PWM controller. The controller is designed to run both fans at the same speed. To do what you ask you would need to totally change the means of fan control.

Alan

 

Yes,
I would like to totally take over “fan control” & have one unit constantly running and the second turned on manually by me.
i can handle it

 

When I had a fan switching issue years ago and a long way from home I bought a cheap relay and connected it to the sidelight wiring so I could switch the fans on when stuck in traffic just switching the sidelights on. I took the fan power feed off the hotpost and a fused line to the fan motor. Worked perfectly.

 

One thing I would suggest is to put the new relays in a position thats ahead of the fans,
or bolt them to the fan shrould and as hi up as possible,
from some of the installs for fan controllers/relays I have seen ,
once the fans start spinning in wet weather conditions,
the relays will get soaked and thus have a short (pun intended ) life.

 

You can use (rather like the weatherpack connectors), but use 40A for this duty for longer life. I'd suggest you have control over both fans so the one that always runs while driving isn't always the same one. (switch this on the low power side). Note that in some conditions you don't need any fans (cold ambient @ speed) so the 'always runs' should perhaps still be thermostatically controlled to save power - you could add a (low power side) bypass switch if you are worried about fail modes & redundancy. Is this because the stock controller failed? or its providing inadequate cooling?

You can keep the stock fuses - intercept the feeders at the existing controller Pins 1 & 4 come from the fuses. If you cannibalize a stock controller and ripped out the guts - you could use that to make all the connections (to power and to the fans (+ drive on pins 5/8), ignore the inputs from the PWM controller) and keep the wiring 100% stock, allowing for reversion just by adding back a stock controller. Not sure how easily you can find a (damaged) fan controller? all you really need is the connector. You'd need 2 x 40A relays, a suitable thermostat and some suitable switches, the wiring to the switches can all be small gauge, getting to the cockpit is a little challenging - I like the pass through right near the wiper motor mount... All the switching should be on the positive side for this because that is considered normal for this type of config.

Since losing cooling fans in Phoenix in summertime is a big deal I do have a backup. My dual feeder pair from the stock controller plug in to a main connector on the fan shroud. Connected to this in parallel I have the 4 fan wires connected to 30A insulated banana sockets at the top of the shroud. This lets me check the PWM fan feeders while running - but if I disconnect the main dual feeder plug I can also use these to power the fans from a similar set of banana sockets next to the jump post (connected to the jump post & GPIII). I have 2 pairs of 30A leads with inline 30A fuses. These can power both fans directly in parallel at full speed. I also have a short connector that allows connecting the fans in series for less than half power on both. Never used it for real driving yet - but always good to have backup plan. The jump post power connectors are also handy to have for quick test connections (these are the same as DVM style meter connections). Since this is all primary heavy gauge power wiring it must be done well and carefully (or not at all).

Alan

 

I am assuming you just have a set of S4 radiator fans and retrofitting them to your 85?

If so, that is an easy proposition. There is also now a good fan controller on the market that can carry the capacity of both stock or other high-current fans:

PWM Controller – Creative Werks Inc.

If you are using the factory controller and output stage, then you do need some creative wiring. As suggested, you can just pirate the output from the factory amplifier and feed the harness, or you can de-pin the connector at the controller in the cabin, and wire some relays to just feed the amplifier a straight voltage. I made a post a couple years back about driving the gates in the controller at a higher voltage.

Clarifying the entire setup would be helpful.

Hans

 

No this is for my 89-
i wish I knew where to get a custom radiator shroud that would work with more efficient aftermarket fans-

i actually do have an override switch in my 85 already, after a Belt Parkway situation coming home from Frenzy.
Long heavy duty alligator clip saved me that day-
(am essential in the road bag)

 

Indeed much of what I wrote assumes you actually have an S4, if you are just fitting S4 fans to an earlier car the details mostly won't apply - but the concept still does.

Alan

 

For the 89, you can depin the connector at the controller, and just feed the fan-amp input pins to drive the gates. This will totally ignore all the other inputs from the controller.

You do need to feed the gate higher than system voltage to get full output. Info on the testing I did a couple years back here:

Fun with 87+ Fan Output Stage - Rennlist - Porsche Discussion Forums

So, get yourself an adjustable buck/boost regulator, set it to ~16.5v, and use that to drive pins Sig1 (Con1 Pin6) and Sig2 (Con1 Pin8).

I believe the fan amplifier has constant power, so any time that Sig1 or Sig2 is driven, the corresponding fan should run, independent of key position.

 

The final stage is indeed un-switched constant power so in this case you'd need ignition/accessory supplied controls

Alan