E fans wiring & ewp

Have a little project

Skoda fabia 6y with a 1.8t 20v on stock management

Due to space in the engine compartment I need to put slimmer fans (brush less spal?)

Issue im having is car has dual fans that have dual speeds

(1 fan operates with switching of AC)

How would I go around wiring the new fans without the original controller(relay)

And control a ewp do i need to have it controlled via pwm or can I have it connected to terminal 30???

Any help appreciated

Hey Khitaam,

If you can't fit a brushed thermo fan and brushless is your only option for the space you've got, you'll need to factor in control. You can't simply turn a brushless fan on with a relay. You need a dedicated controller for brushless motors, since the motor itself requires a PWM signal to run, not just a 12V feed. These controllers will also have their own systems for controlling speed, which answers your speed question for the fan side.

However, if you find a brushed fan that fits, you have simpler options for control. For two-speed control across two fans, it's common for OEM setups to use a relay arrangement that wires the two fans in series for low speed and parallel for high speed. In series, each fan effectively acts as a current-limiting load on the other, dropping the voltage each one sees and slowing them down. For high speed, the relays separate the two circuits and power each fan in parallel at full voltage.

Personally, I prefer a simpler approach: wire one fan as the first stage, switched on by a thermal switch in the cooling system (set to trigger at say 90°C), then a second thermal switch (some have two circuits built into one unit) that brings the second fan on at a higher temp, say 95°C. It won't give you true variable fan speed, but it does give you staged cooling and keeps current draw down at lower, less critical temps.

Regarding the water pump, it's not recommended to just run it direct off a constant 12V at full speed all the time, since that wastes power and overcools when demand is low. A speed-controlled setup is the better option, either through an aftermarket ECU/PDM with a fan/pump output, or a dedicated controller like the Davies Craig EWP digital controller, which varies pump speed based on coolant temperature. Worth checking the control method of whichever controller you land on, since not all of them work the same way. Most of these controllers (or an aftermarket ECU/PDM) will also let you control the fans from the same unit.

It's difficult for me to advise on wiring into your specific OEM system without more information, ideally some basic wiring diagrams of how you're planning to set things up. If you can post those, I'd be happy to go over them and give any advice.

The original wiring diagram

When I said ewp I meant an auxiliary water pump to aid water cooling on engine shut off

I can't be fully confident going off those diagrams since the dashed lines specifically indicate a non-AC vehicle, and you've mentioned the car has AC. So take the below as a general guide rather than a confirmed match to your exact car.

From what's shown, the two stock fans each have separate low and high speed inputs, low speed runs through a built-in inline resistor to drop voltage and slow the fan, high speed feeds it directly.

If you're removing the stock fans and control unit, I'd keep it simple: two relays, one per fan. Wire the common side of the thermo switch to ground, have the low-temp contact switch the ground side of relay 1 (first fan), and the high-temp contact switch relay 2 (second fan). It won't give you true low/high fan speed like the original setup, but it works as a low-temp/high-temp staged system, which is effectively how most aftermarket ECU-controlled setups do it anyway, the only difference being the ECU switches the relays instead of a thermo switch.

For the AC side, that depends on what signal you've actually got available on the car, it's not something shown on these diagrams so you'll need to identify that yourself (AC compressor request wire, AC clutch trigger, etc). Once you've got it, the easiest way to bring it in is a third relay switched by that AC signal, with its output wired in parallel with relay 1's output to the first fan. That way either the low-temp thermo switch or AC being on will turn fan 1 on, whichever comes first.

If it's simply an auxiliary pump for shutdown, you can power it directly with 12V, no speed controller needed for this use case. If it was my car, I'd wire it with a timer relay, triggered by ignition off, that then switches a normal 4-pin relay to turn the pump on, or use a changeover relay triggered by ignition, using the NC contacts to complete a circuit from the low-temp thermo switch to the EWP relay. This keeps the pump running with the ignition off until the temp drops below the low-temp threshold. I can draw up a simple diagram if that helps.

Post some wiring diagrams of what you're planning and I'll go over them with you.

Thank you for the response Caleb

I did notice the dashed lines being for non AC cars but I'm not able to find another diagram for my vehicle strangely

Once I get the car out the storage lockup I will post some diagrams of what I plan to do for the fans and aux pump