cooling fans

Hello,

I'm wiring up the old Porsche cooling fans today. I was wondering if there was a thread or schematic bumping around here that would be able to help me out. Would the low speed relay turn just one fan on and then the high speed relay turns both on? Or is actual speed control? Since I'm using the stock fan housing I should be able to splice into stock harness and use the Porsche plugs, right?

any advice on this project would be great,

Thanks,
Luke

Thank you very much

When the ECU triggers the high speed relay does it stop sending a signal to the low speed relay or does it send both signals at once?

Heres what I made for running dual fans (hi/low). You will make this harness yourself. It looks difficult but its not really. Just built on your benchtop and then install. Double check these pins in your schematic. Im not sure if they are exactly the same. Let me know if you go this route how it all works out!

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So "low speed" just means only one fan is running and "high speed" means both fans are running. There isn't any difference in rpm?


Also, I don't have a lot of time to study what you have drawn below but quickly it looks like the low speed signal from the computer does indeed cut out as soon as the signal for high speed kicks on, right?

Are you controlling the dual fans with the stock LS computer? This is what Im assuming. If you are, the stock LS computer is designed to run 2 fans with 3 relays. The computer controls what the fans are doing: 2 fans Low, 1 fan High, 2 fans High. As far as when or why the computer does this is up to the engineers.

If you are thinking of using the factory wiring and plugs... Bypass the big honkin resistors that Porsche used for low speed that are located above the glove box. There are two of them..

That was vague in that I left out that the LS computer is sending GROUND to these relays nor +12vdc. This is important in understanding why you must use 3 relays to use the LS computers cooling circuit.

"The electric cooling fans are controlled by the PCM. The PCM controls the ground path for the three cooling fan relays. The relays are used to control the high current flow to power the cooling fan motors. Both fans operate together. When minimum cooling is required, the PCM energizes cooling fan relay #1 and both fans operate at low speed, since the fans are connected in series through cooling fan relay #3. Cooling fan relay #2 is open (not energized) and is not used for low speed operation of the fans. When maximum cooling is required, the PCM energizes all three cooling fan relays. The left fan is still powered through cooling fan relay #1, but is now grounded through cooling fan relay #3. The right fan is now powered directly through cooling fan relay #2 and both fans operated at high speed.

The PCM will also enable the cooling fans after the ignition is turned off. When the engine coolant temperature exceeds 113°C (235°F) and the ignition is turned off, the cooling fans will be enabled on low speed for 150 seconds.

Low Speed Cooling Fans
The low speed cooling fans are controlled by the PCM based on the following inputs:

The A/C system.
The Engine Coolant Temperature (ECT) sensor.
The Vehicle Speed Sensor (VSS).
The PCM will turn the cooling fans on low speed when any of the following conditions exist at idle:

Certain PCM Diagnostic Trouble Codes (DTCs) are set.
The ECT above 108°C (226°F).
The A/C high side pressure above 215 psi.
Once the low speed fans are turned ON by Engine Coolant Temperature, the PCM will turn the fans OFF when that temperature has dropped about 4°C (7°F). If the low speed cooling fans are turned ON by high A/C head pressure, the PCM will turn the fans OFF when the pressure has dropped to 190 psi. The minimum ON time for the low speed cooling fans is 50 seconds.

The cooling fans are turned OFF at certain vehicle speeds. Adequate airflow through the A/C condenser and radiator occurs with vehicle movement to properly cool the A/C refrigerant and engine coolant without the assistance of the cooling fans.

High Speed Cooling Fans
The High Speed Cooling Fans are controlled by the PCM based on the following inputs:

The A/C system.
The Engine Coolant Temperature (ECT) sensor.
The Vehicle Speed Sensor (VSS).
The PCM will enable both fans on high speed when any of the following conditions exist:

Certain PCM Diagnostic Trouble Codes (DTCs) set.
The ECT above 112°C (234°F).
The A/C high side pressure above 248 psi.
Once the high speed cooling fans are turned ON by the Engine coolant temperature, the PCM will turn the fans OFF when that temperature has dropped about 4°C (7°F). If the high speed cooling fans are turned ON by high A/C head pressure, the PCM will turn the fans OFF when the pressure has dropped to 208 psi. The minimum ON time for the high speed cooling fans is 30 seconds. "

wow, great info. I'll let you know what I do in the end!

Thats alot of inputs for two fans. Does it make much difference with the a/c if I have a stand alone on my fans. They are set to turn on at 180F. I will be installing an a/c system next summer if all goes well this winter with the new install and am trying to figure out if I need to wire the fan to the ecu.

My setup only has one big fan. I would have to install a pusher fan on the front for the a/c.

Thats alot of inputs for two fans.

Its really quite simple when you break it down per relay.

Does it make much difference with the a/c if I have a stand alone on my fans. They are set to turn on at 180F. I will be installing an a/c system next summer if all goes well this winter with the new install and am trying to figure out if I need to wire the fan to the ecu.

But of course! When the AC is turned on, the engine will bog down a bit. Although most swappers will run the AC behind the PCMs back, its a shame since the wiring is not any harder than wiring up a stand alone and letting the engine struggle at idle. Bottom line, alot of guys dont wire the AC to the computer. These guys have to manually turn up the fan speed, engage the AC clutch and monitor the engine and AC system all the while running a bogging idle. Three relays for that?!?!

My setup only has one big fan. I would have to install a pusher fan on the front for the a/c.

Well, you would need just two relays then. But I dont think youre gonna get a pusher in there if the radiator and condenser are in the stock location. Wait....youre not thinking of installing a pusher AND a puller together are you????

Well, you would need just two relays then. But I dont think youre gonna get a pusher in there if the radiator and condenser are in the stock location. Neutral Wait....youre not thinking of installing a pusher AND a puller together are you???? silent

WHAT!?! is this a diesel or something? u got turbos or a supercharger? i got a gmc 454 5 speed and it got 1 push 2 pulls and it still get hot

What if I just plugged the Porsche thermo switch back into the harness and screwed it into the radiator? that would use all the stock relays and everything. That's how I got to take the car for a test drive yesterday, I just put a jumper in the thermo-switch plug to keep the fans on

That's what I did (using the stock Porsche fans, harness, sensors, and relays) and it seems to run fine. AS far I can tell, the only advantage to having the PCM control the fans would be that the PCM can be programmed to bring the fans in at a lower tempeerature if you are having cooling problems.

I am also using the stock Porsche AC, though I control the AC request signal through the PCM (using a GM AC pressure sensor) so that the PCM knows to bump the idle slightly when the AC is on. My stock fans then come on at the appropriate AC compressor head pressure (using the Porsche AC pressure sensor).

maybe that's the route I'll go then, I'm not going to have AC.

Thanks all.

On the Porsche boards there is daily someone having a fan issue related to the thermoswitch or relays. I am going with my own wiring.

Luke if I remember Maine form when I was little, it never did get extremely hot. So ya a/c is not a big issue for you, just a heater. lol

exactly, I'm putting in a heater but not an AC

i used factory fans and wiring on mine but added a manual switch to the temp sensor wires to operate fans manualy .works really good

yeah, I've got a manual switch wired into the factory wiring right now. Is that all you've got? Or do you have a temp switch too.

Factory fans, relay and thermo switch. I put a new thermo switch in 10 years ago.....no problems so far.
If your relay and swtich are original, which most are, I would replace at least the thermo switch and get a back-up used relay...

i have a temp switch hooked to original wiring but also have a toggle hooked in to manualy operate.i use l the original relay wiring fans and just put a new temp switch to sense engine temp .it works great that way.even if you dont run ac if you turn ac switch on inside the car the fans will turn on because its also tied into the fan relay

ur gonna have an a/c, just roll down the window, and make sure your going fast enough to catch the cold air.

If anyone is interested I have a wiring diagram I created that I need someone to be a test mule... Someone asked me to figure out how to use the GM A/C stuff, without having to install the GM pressure sensor. The way i have it wired still has the Porsche sensor which i believe is just a low pressure cutoff, so you are protected there. Anyway, if someone wants to try it out just let me know.

Mark

I am not there yet, but I would like the diagrams. Post it up. Thanks.