Scavenger Fan

[roosmith]

I did try not to start another thread but couldn't find answers to what I have.

My scavenger fan never comes on so on the never ending list of things to do was diagnose but probably do the modification to manually override. I found the connector everyone talks about, unplugged it ready to find a suitable resistor and before I put anything in there the fan came on. The glowplug light flashed to say there was a fault as people said it would but I thought that was when you shorted the connector or put in a resistor? Turning the engine off left the fan on for quite a long time, starting up again stopped the fan and it only cut back in again when the temperature was back up, as though it was measuring temperature somewhere else. As soon as I plugged the sensor back in, it stopped.

I had a little play with some resistors but either I was getting confused about what sizes I had and would work or nothing makes a blind bit of difference.

Have I lost the plot after 2 days working on the Bongo or is there something that would cause this?

[g8dhe]

The fan works as you have now shown, its just that it doesn't need to come on very often, so I wouldn't really get too worried about it. The only other possibility would be the sensor is faulty, but if you have a meter check its resistance and someone with a diesel manual can probably tell you if the value is in the right range.

[Bob]

Am I right thinking these come on with the aircon?

[roosmith]

Thanks Geoff. I thought that if you disconnected the sensor it would see an open circuit and stay off. It was only when the resistance got high that it would come on, hence putting in a resistor.

Without fully understanding the way it works if you disconnect the sensor and the fan comes on, does sound like a faulty sensor though I agree.

Just confusing as everyone before has spoken about shorting the pins with a resistor to get the fan on

Bob, I think it is just the radiator fans that come on with the air-con not the scavenger (but as above my understanding isn't brilliant at this time).

I'm sure the scavenger doesn't work properly as when I got it on yesterday I'd definitely not heard that noise before. We have got about its trigger point many times towing the caravan and it has never come on by it's own accord. Hmmmmm

[Simon Jones]

Am I right thinking these come on with the aircon?

No, scavenger fan is controlled exclusively by the sensor by the handbrake. The rad fans will come on with the aircon though.

To test the sensor:

[mikeonb4c]

I find the TM2 engine block temp gauge and a scavenger fan over-ride switch/circuit a perfect combination. I have complete control over putting it on to ensure a cooler cab (not just a cooler engine bay, though I like the idea of ageing components not having to work in overly harsh heat) and the fan gets a little exercise now and then. And no more worries about old sensors that might have stopped working properly.

[JoeC]

Could somebody write up an Idiots Guide To Installing A Scavenger Fan Override Ride and put it in the Fact sheet area please?

[Northern Bongolow]

the way forward is to test the sensor values shown by simon, it may be working fine but the scavvy fan may be trying to seize up so require lower than the trigger point resistance reading to actually start the scavvy fan turning.

ps ive never seen one trigger and run naturally ever and ive bled and messed with bongos for 8 years.

[mikeonb4c]

Could somebody write up an Idiots Guide To Installing A Scavenger Fan Override Ride and put it in the Fact sheet area please?

There is a mucher slicker way that involves bypassing the sensor/relay by the handbrake. But when i did mine no-one had identified that way of doing it and i simply ran a fresh fused power feed to the fan. I learned that 15 amps was insufficient (fuse kept blowing) so upgraded the wire and fuse to 30 Amps. It seems to work fine but the sensor bypass method makes more sense i reckon.

[cmm303]

Could somebody write up an Idiots Guide To Installing A Scavenger Fan Override Ride and put it in the Fact sheet area please?

There is a mucher slicker way that involves bypassing the sensor/relay by the handbrake. But when i did mine no-one had identified that way of doing it and i simply ran a fresh fused power feed to the fan. I learned that 15 amps was insufficient (fuse kept blowing) so upgraded the wire and fuse to 30 Amps. It seems to work fine but the sensor bypass method makes more sense i reckon.

it would be safer not to remove the sensor activation. That way you still have the heat sensed operation as a fallback should the manual override not be operated when it really is needed.

Personally, I can't help feel that if the scavenger fan really needed to cut in at lower temps then the Mazda designers would have triggered it thus.

If the sensor is tested as already suggested, the rest of the system could be tested using a variable resistor / potentiometer to replace the sensor. A bit more controlled than heating the area with an hairdryer and not knowing how hot you have to go to before declaring it working or not working!

[mikeonb4c]

Absolutely. Neither method disables the sensor just provides the option to over-ride it. Although i'm sure you're right about Mazda knowing what they were doing, a 20 year old Bongo is probably working well beyond its design life so combined with a TM2 engine block temp gauge the over-ride option is very handy. Also, I think Mazda will be primarily concerned with engine wellbeing whereas i'm interested in cool passenger accommodation in hot weather (esp if/when stuck in traffic). In that situation the scavenger fan can
facilitate a substantial drop in temperature in a matter of minutes. Nice to see it being used to good effect.

[Tony x]

Could somebody write up an Idiots Guide To Installing A Scavenger Fan Override Ride and put it in the Fact sheet area please?

Here's a simplified circuit diagram:-



The fan will come on and off when driving using the switch but, with the ignition off and key out, switching the fan on will result in it running for about 5 minutes or so even if you then turn the switch off.

[Fassi]

I've the same setup as Tony x and works a treat.

[JoeC]

Could somebody write up an Idiots Guide To Installing A Scavenger Fan Override Ride and put it in the Fact sheet area please?

Here's a simplified circuit diagram:-



The fan will come on and off when driving using the switch but, with the ignition off and key out, switching the fan on will result in it running for about 5 minutes or so even if you then turn the switch off.

That's easy enough for me to understand - thanks.

What wattage of resistor is required?

[Fassi]

Could somebody write up an Idiots Guide To Installing A Scavenger Fan Override Ride and put it in the Fact sheet area please?

Here's a simplified circuit diagram:-



The fan will come on and off when driving using the switch but, with the ignition off and key out, switching the fan on will result in it running for about 5 minutes or so even if you then turn the switch off.

That's easy enough for me to understand - thanks.

What wattage of resistor is required?

I'm sure a 1/4 watt wasn't enough. some rough sums give 0.36 watt but that is rough. I'm using a 1 watt if i remember right.