ag9v

I tried the radiator fan mod on my 2000 couple this past Saturday, grounding pin 85 of both relays 20 and 22 but it didn't turn on the high speed fans... rather, it seemed to shut off the fans.

I tried multiple combinations of settings within the car, like grounding the relays with A/C on and off, with the entire climate control on and off... Nothing worked.

When the relays were not grounded (pre-modification), I found that the radiator fans came on when the A/C compressor was turned on. Grounding the relays with the A/C on produced a spark, then the radiator fans would shut down.

With the unexpected results and preferring that I not screw anything up, I stopped work on the mod.

Has anyone else experienced this fan behavior or did I overlook something?

1999Porsche911

Verify that you are in fact using the correct pin using a voltmeter. Remove relay and ground the hot in the slot for the relay. Fan should start immediately. You will not blow anything trying each pin.

ag9v

Thanks for the feedback. I'll try it out the next time I have a chance to take the footwell apart. I assumed the relay diagram on the surface of the relay was aligned with the pins on the bottom of the relay but I may have made an incorrect assumption.

Do you have any numbers on how much amperage is estimated to flow through the ground wire? I want to make sure I chose a switch with an adequate capacity.

1999Porsche911

I use a 10 amp switch. Actual amp draw is probably half that.

BlackCab996

OK, I'm going to ask a really stupid question, so forgive me. Would this also mean that you could activate the fans if you turn on the AC at its lowest setting? And if yes, could this help to accelerate cooling the engine, or is the offsetting amount of pull from the AC enough to heat things right back up?

1999Porsche911

AC is either on or off, only the amount of cool/warm air mixture is changed. Running the AC will initially make the engine cool down, but it will slowly run up again due to the increased load on the engine as well as the fans cycling between low and high speed. The ONLY way to keep the coolant around 195F in stop and go or slow driving in warmer temps, is to keep the 2 front fans running full speed. There is simply not enough radiator surface (including 3rd radiator) for natural ariflow to cool the fluid without forced air for speeds under about 60 mph..

BlackCab996

That makes sense - I actually like the idea of your modification, as I noticed some warmer temps during the hot summer that we have had. Plus, Los Angeles freeways are often stop and go traffic. I just need to find someone local that can help me with this mod. I become fearful with electrical wiring projects.

1999Porsche911

Just remove one of the fan relays, insert a 16/18 gauge wire in the #85 socket and put the relay back in. Now, touching the other end of the wire to any ground on the car (bolt,frame, etc) will start the fan. Removing it from ground with stop the fan. Now all you do, is get a switch and connect the wire from the replay to one side and another wire from a ground to the other side of the switch. You now have a way of turning the fans on and off. All you have to do is decide where to put the switch.