Chris(MA)

hey folks, I believe there is a mod to link both high and low speed coolant fans together so they come on in sync. Does anyone have a link or pics to share on this? I think it's a jumper between relays.

i searched and can't seem to find it

ion_berkley

I think you are confused, the low fan speed is achieved by dropping the voltage to the fan across a high power resistor (They are prone to failing, another 996 gotcha). So when the fan is in high speed mode the nominal 12V drives the fan directly, and when it's in low speed mode it's feed in series with this resistor.

billh1963

From an older archive...


Originally Posted by 1999Porsche911 View Post
If you want your engine to remain cooler (190F rather than 220), simply do my fan switch mod. No need for heaveier 3rd radiator.

Radiator Fan and Engine Compartment Fan Switch Mod


The 3.4 996 runs extremely hot when driving around town in temperatures higher than 75 degrees. This mod is a way to reduce coolant temps back to a safer level, helping to reduce oil temps and improving performance.

The mod consists of installing a switch that will allow you to turn on the high speed radiator fans at any time, while maintaining the automatic operation of the fans. We do the same for the engine compartment fan.

Radiator Fans

Connect a wire to the ground of the 2 high speed fan relays located on the relay carrier located in the driver’s side foot well. The relays are #20 and #22. Feed this wire to where your switch will be located. Connect the wire to one side of the switch. Connect another wire from the other contact on the switch and then connect the other end of this wire to a chassis ground point.

With key on, this switch will now immediately turn on both radiator fans providing maximum cooling. When you turn the key off, the fans will continue to run for about 5 seconds until the relay shuts down. Your fan operation remains normal when the switch is off.

Engine Compartment Fan

Connect a wire to the ground of the relay located in the relay carrier behind the passenger seat, driver’s side. Relay #8. . Feed this wire to where your switch will be located. I simply fed the wire along the driver’s side of the car and under the door sill. Connect the wire to one side of the switch. Connect another wire from the other contact on the switch and connect the other end of this wire to a chassis ground point.

With key on, this switch will now immediately turn on the fan drawing air into the engine compartment. When you turn the key off, the fan will continue to run for about 5 seconds until the relay shuts down. Your fan operation remains normal when the switch is off. This mod helps keep the engine compartment much cooler when driving around town and is particularly beneficial to any engine that draws its intake air from inside the engine compartment, such as the EVO SC.


If you are adventurous, you can automate the operation of these switches so they will switch off at a specific speed, or operate when vacuum is present only, etc. You can choose any style switch you want and even use Porsche switches. I simply used 2 toggle switches that I installed in the batwing,

Jim

Chris(MA)

Thanks everyone, I also found out about the cracking of the low fan resistor, I will have to check mine out and replace if broken

Volkert

I think it is a pretty nice safety feature to have that switch available to turn on the fans to highspeed if you think it is required. I have been sitting in the car wondering when finally those fans kick in; not so nice. Having said that, first and foremost check if the cooling system is working as designed; I had one of the fans not kicking in at low speed, and that explained why I saw the cooling temp rise to 225F before anything happened.... In my case it was not the resistor but a relay issue.

dkraige

FYI it's pretty easy to check the low and high speed functioning of both fans by just jumpering each of the relays (19-22) one at a time.

Turn the ignition key on, and then attach a jumper wire between terminals 30 (+12V) and 87 (fan) on each one (one at a time!) You should hear the fan run as long as the jumper is connected.

19 left low speed
20 left high speed
21 right low speed
22 right high speed

If a low speed doesn't work, but the high speed does, it's probably the resistor, or wiring.

If neither speed works, it could be the fan, fuse, or wiring.

If all this works, but then it doesn't work in practice when you turn on the AC or the motor gets hot, then the associated relay is bad.

I performed this test the other day and found my right low speed not working, but everything else is good, so I'm reasonably confident I just need to replace that resistor.