quick question re rad fans

[Northern Bongolow]

if you take off the large flat air scoop when you open the bonnet and look behind the radiator top you will see where the fans plug into the wiring loom, there are 2 (if i remember right) large plugs one at each end of the front radiator, inside, unplug these and switch the fans to operate then test for live with a meter, and test the earth, if ok then put a 12 volt supply to each fan in turn to see if they come on. WATCH YER FINGERS.

[g8dhe]

The two fans are wired in parallel so should work at the same time;

They are both controlled together and there are at least two different speeds.

[Northern Bongolow]

forgive me geoff but can you check that, im fairly sure it goes 1 on then 2 on, then both fast. or is it 1 on just with aircon.

im not good enough with the diagrams to spot the differences if the control /on off is on the neg side or temp triggered.

[helen&tony]

Hi
That was my understanding, too, Ady, from when we were checking out the system years ago!...but I wonder if there are differences in individual years of manufacture?....When I changed my fan sensor as a matter of routine service, the fans seem to come on at different sequence to previously...namely, they come on at a given temperature and seem to stay???....All temperatures are the same as before...block, head, water, bottom hose....no different, but the fan sequencing seems out?...2 possibilities...the internal working of the sensor is different, or the new unit is naff
Cheers
Helen

[g8dhe]

I must admit that was my expectation when I checked the diagram! But the diagram shows all 4 connections directly connect between the two fans - then going off to the relays or earth so that the two operate together - do remember these fans are NOT standard they have two sets of windings and so can do two speeds, but diagram wise they are in parallel and so should come on together. This also goes for all three versions that are currently available on the diagrams covering 1995 thru to 1999. I can't rule out later versions being different of course.

[Northern Bongolow]

cheers geoff.
as part of bleeding a bongo i run /test everything, including the fan trigger temps, next time i will look more carefully.

[g8dhe]

Do let me know, I've not yet found any errors in the diagrams, other than possibly some colour differences, but mucky wires and colour blindness could also be the cause!

[cushers]

Finally sorted.
Thank you all for the advice.
I found that the problem was a connection that didn't make the contact when fully engaged. I only found it when reattaching the feed loom.

[Northern Bongolow]

was that one of the 2 plugs behind the top of the rad.

[cushers]

It was indeed N-B.

They appear black and yellow on my Freda 95 2.5 td

[Northern Bongolow]

thanks for the reply, it may just help others following this in 3 years time.

[cmm303]

The two fans are wired in parallel so should work at the same time;

They are both controlled together and there are at least two different speeds.

forgive me geoff but can you check that, im fairly sure it goes 1 on then 2 on, then both fast. or is it 1 on just with aircon.

im not good enough with the diagrams to spot the differences if the control /on off is on the neg side or temp triggered.

cheers geoff.
as part of bleeding a bongo i run /test everything, including the fan trigger temps, next time i will look more carefully.

I have the checked the fan operation on my Bongo with a resistor connected to the sensor lead instead of the sensor:

Open Circuit: Fast idle, then after a short delay both fans high speed
>180 ohms: No fans
180 ohms: Both fans, normal speed
150 ohms: Both fans, high speed
100 ohms: no change, as 150 ohms
Short circuit: not tested.

I did the test by reducing the resistance until something changed (because we are normally interested in when the fans come on), then backing off a very small amount, not enough to reverse the step. The variable resistor was then disconnected and measured. Hard to be exact about the accuracy but I'd suspect that it is within 10 ohms and quite possibly within 5 ohms.

Relating this to some empirical data from another member, jimmo62, which he kindly shared. He measured a Mazda sensor resistance of 200 ohms at 104.3 deg C. Extrapolation suggests that 180 ohms would be at 106 -107 deg C. Explains why waiting for the fans to kick in is buttock clenching.

[Northern Bongolow]

what !!!!!. .

i got the clenching bit.

[cmm303]

For the benefit of anybody reading this thread at a later date, something does not stack up.

In more than one older thread (and there are loads on this subject) - this one for example - it is agreed by the great and good that the spec for fan operation is:

96 deg - fans at low speed
104 deg - fans at high speed

In my post above, the Mazda temp sensor resistance measurements combined with the resistances at which my fans kick in don't align with this at all. Without an independent means of reporting absolute temp I can't say much more than point this out as a caveat.