Scavenger Fan - manual over ride switch

[HA106420]

Have just had a play around short circuiting the scavenger fan sensor - i.e. to test the fan works and possibly with the intenion of fitting a switch for a manual override.

However, once the scavenger fan sensor is removed and is short circuited/switched on starting up the scavenger fan, when the short circuit is removed / switched off, the scavenger fan remains on!

How can this be when the circuit is broken once the short circuit is removed?

The short circuit / switch works fine once the scavenger fan sensor is re-fitted. i.e i am able to switch the scavenger fan on and off - but just wondered how the scavenger fan remained on when there was no complete circuit in the scenario outlined above.

[pippin]

Because it is relay operated via the ECU.

[mikeonb4c]

Pippin - since you're here, why do you think Cocos mechanic said he couldn't fit a switch that would allow the fan to operate either via the sensor or by a manual over-ride. Also, if it is ECU controlled how is it ever going to be possible to provide manual on/off over-ride I wonder.

[pippin]

By not tinkering with the sensor input side of the ECU.

Simply putting a three position changeover switch in the supply to the fan would be the easier.

ON - normal control

OFF - completely

ON - powered from leisure battery.

That was my goal - but then I sold my Bongo!

[dandywarhol]

While we're on the topic - I posted in a previous thread that the scavenger fan came on at 180 deg.C........bollox! it's 100 deg. I misread the badly translated manual

180 is the max range of the sensor.

Pippin is spot on about the fan being ECU circuited.............I don't think I'd mess about with it - ECUs are expensive

[rwill19050]

Manual override, why would you want to do this, are you having overheating problems ?

Have just had a play around short circuiting the scavenger fan sensor - i.e. to test the fan works and possibly with the intenion of fitting a switch for a manual override.

However, once the scavenger fan sensor is removed and is short circuited/switched on starting up the scavenger fan, when the short circuit is removed / switched off, the scavenger fan remains on!

How can this be when the circuit is broken once the short circuit is removed?

The short circuit / switch works fine once the scavenger fan sensor is re-fitted. i.e i am able to switch the scavenger fan on and off - but just wondered how the scavenger fan remained on when there was no complete circuit in the scenario outlined above.

[helen&tony]

Hi Dandy
I would be inclined to agree with you....maybe, if worried, dunk the sensor in hot water and see if it works at the specified temp.
When the fan turns on , it sends a high volume of air through, and the whole shebang cools quite quickly. I have only found the fan works after a long run in high temperatures, and not normally until you turn the engine off, and come back 10 mins later, when the engine compartment continues to heat....flick the ignition on, the fan starts, start the engine, and moments later it turns off. If it doesn't, then it's a coolant fault, and nothing to do with the scavenger fan.
Cheers
Helen

[mikeonb4c]

Manual override, why would you want to do this, are you having overheating problems ?

In my case, nothing to do with overheating but a desire to stop the engine covers from becoming a 'radiator' on a hot summers day. I end up with aircon on often just to cancel out warming effect of the engine covers. it's not a big issue and I love having these 'radiators' most of the time, but it would be interesting to see if the scavenger would cool it a bit in summer. Also, all components generally benefit from running in a 'not too hot' environment.

PS - Pippin - I think an ON/ON switch would effectively be enough as the position that maintains the original sensor/ECU option will effectively be the same as 'OFF' in the UK climate, plus if the sensor/ECU does think it needs to come on then I guess I shouldn't allow a situation where its advice might be ignored?

[pippin]

Basically my idea was to have the scavenger fan operating normally under ECU control in the NORMAL position.

As mentioned, the engine bay gets very very hot, which is a big bonus in winter - but a pain in summer.

In the ON position I was thinking of powering up the fan from the leisure battery, possibly via a timer to enable forced cooling of the engine bay when stopped after a long run in summer.

Thinking about it, the switch only needs two positions but would need to be double pole double throw DPDT and fairly hefty current-wise unless operated via a relay.

What put me off doing the job was the thought of scrabbling around underneath the engine bay trying to trace the wiring.

[mikeonb4c]

Basically my idea was to have the scavenger fan operating normally under ECU control in the NORMAL position.

As mentioned, the engine bay gets very very hot, which is a big bonus in winter - but a pain in summer.

In the ON position I was thinking of powering up the fan from the leisure battery, possibly via a timer to enable forced cooling of the engine bay when stopped after a long run in summer.

Thinking about it, the switch only needs two positions but would need to be double pole double throw DPDT and fairly hefty current-wise unless operated via a relay.

What put me off doing the job was the thought of scrabbling around underneath the engine bay trying to trace the wiring.

Just reviving this one in case Pippin (or anyone else) is looking in. It seems to me that a simple on/off switch could achieve this. In the ON position the switch simply makes a direct power connection to the scavenger fan (or to a relay which then allows a live feed to the scavenger fan) and so activates it. In the OFF position, the original power supply from the CPU would still be in place and able to activate the fan as per original design. Can anyone see a flaw with this (e.g. current 'back feeding' up the ECU circuit when the new switch is in the ON position - I'm afraid I'm no leccie).

I think I'd take my live feed from an 'ignition live' or 'accessory live' source and power from main battery so there was no danger of leaving the fan on when engine was off and/or key out of the ignition.

[Aethelric]

I got my bongo in early march, so I have not yet had the delights of a hot engine covers on a hot summers day. Most I've had is melted chocolate left in the wee space by the gear lever. But I can't see why the changeover switch would not work. It sounds better than trying to fool the ECU.
While on the subject, does anyone know why the bongo has three temperature sensors? They all seem to to measure essentially the same thing but have different functions (panel temperature gauge, radiator fan, and scavenger fan).

Dave

[mikeonb4c]

Thanks Aethelric - a bit of encouragement to try. Anyone else got a view?

On 3 temp sensors, I can immediately think of two distinct things (1) engine coolant temp and (2) engine bay temp. Scavanger fan will use (2) and rad. fan and engine temp would use (1). To explain the need for two other sensors, is there a need for the fan to sense temp. downstream of the thermostat whilst engine temp gauge needs to have hottest temp, which will be upstream of thermostat. Yes, that must surely be it. Anyone able to confirm/correct that?

[Aethelric]

Thanks Aethelric - a bit of encouragement to try. Anyone else got a view?

On 3 temp sensors, I can immediately think of two distinct things (1) engine coolant temp and (2) engine bay temp. Scavanger fan will use (2) and rad. fan and engine temp would use (1). To explain the need for two other sensors, is there a need for the fan to sense temp. downstream of the thermostat whilst engine temp gauge needs to have hottest temp, which will be upstream of thermostat. Yes, that must surely be it. Anyone able to confirm/correct that?

I think the only bit downstream of the thermostat is a hose Mike It must have something to do with different bits of the engine though.

[mikeonb4c]

Thanks Aethelric - a bit of encouragement to try. Anyone else got a view?

On 3 temp sensors, I can immediately think of two distinct things (1) engine coolant temp and (2) engine bay temp. Scavanger fan will use (2) and rad. fan and engine temp would use (1). To explain the need for two other sensors, is there a need for the fan to sense temp. downstream of the thermostat whilst engine temp gauge needs to have hottest temp, which will be upstream of thermostat. Yes, that must surely be it. Anyone able to confirm/correct that?

I think the only bit downstream of the thermostat is a hose Mike It must have something to do with different bits of the engine though.

No doubt one of our mechanical geniuses will be along to explain it in due course