Scavenger Fan

[the1andonly]

Ive used 3 1kohm 1/4 watt in paralell

[Tony x]

I seem to remember using two 800 ohm rated at 3 watts each resistors in parallel.

[vitus992]

Many thanks for the drawing, I have created the override myself.
I have used a 390 ohm resistor though, I hope this is ok, testing everything seems ok at the moment.

Daren

[nth]

I was thinking of putting in a switch to operate the scav fan too. I was thinking along the lines of just fitting a switched earth (which appears to be normally operated by the ECU) to the primary side of the relay. Has anyone done it this way & does it still cause the glow plug light to flash ? Or can anyone think of any downsides of doing it this way ?

[Bongolia]

Interesting,why the resistor?

[Gasy]

Think it puts out the same amount of power as the engine temp sensor
Or something like that
When the engine sensor is activated by a hot engine , think some people have measured it's not 12v coming out
But by by passing the sensor with a switch we are sending 12v
So they put in resistors
Mines had no resistor for years keep meaning to do it

Interesting thing was
Without the resistors if you switch engine off and remove keys with scavenger switched on
You get a fan over run of a few mins ( handy if leaving a hot engine )
But with certain sized resistors this did not happen

[g8dhe]

The Sensor is a Thermistor- Thermal Resistor - its resistance varies with temperature its a Negative Temperature Coefficient (NTC) type so as the temperature goes up the resistance comes down so a Short Circuit looks like an extremely high temperature and so the ECU commands the fan on until the temperature reduces - however the ECU also sets a time limit as the last thing you want is a flat battery in the morning when you come out due to a fault!

Bear in mind that the scavenger fan only moves the air out from around the engine compartment, it doesn't really cool the engine as such but stops the compartment and the seats above from getting too hot!

[Gasy]

It does drop my engine temp when I use the scavenger fan switch
It will drop from high 90s to high 80s in a few mins
You can also watch the bottom hose temp drop as well when scavenger is on
So by moving the hot air out from around the engine it does drop engine temp

[Bongolia]

So the ECU uses mapped resistances to trigger the cooling fans as the temperature increases? Low speed then high then scavenge?
So one temp sensor for all fans?

[Bongolia]

Just realized there were previous posts and that the scavenger fan is triggered by a separate sensor in the engine bay.
So go that now thanks.

[Bongolia]

I still cannot understand why it needs a resistor though,once the ECU sees the resistance below a certain level it triggers the fan until the resistance rises to a certain level then offs the fan.
So by switching it you effectively short the circuit. The ECU sees the resistance as below the trigger threshold and triggers the fan, as it will never see the resistance increase while the switch is shorting the circuit it will continue to run the fan. Once the short circuit is removed ,switch open,it will revert back to closed circuit wouldn't it?
So why the resistor?

A possible answer to Roosmiths comment about the fan firing when he disconnected the sensor.
It is not uncommon for the ECU to have a function that triggers the fans to run when open circuit is seen. If that where so on the Bongo setting a switch to open the circuit could be another method although it may set up a fault code?

[Bongolia]

Have I answered my first question in the last part my post.
Is it stop a fault code flagging up?

[Bongolia]

Message to self,
search effin forums first!!

[Gasy]

You do get a flashing fault code / light on the dash when switch is on
( not the hold light the other 1 )

[nth]

This is how i done it without a resistor & no flashing fault warnings.
http://igmaynard.co.uk/bongo/forum/view ... an#p679915