Lower temperature Fan Relay Mod

[wmax351]

The title says it all. I it is very possible to modify the fan relay such that it activates the fan at a much lower temperature, perhaps even an adjustable one.





I will need to look at the other side of the relay board (I think I may have and extra one at home). Basically, the MC3302P is a standard quad comparator. It supplies +12v via a bias resistor for the coolant temperature sensor, and compares the voltage from in between the bias resistor and the CLT sensor, to one in between each of two pairs of resistors that are equivalent to the bias resistor/CLT sensor at 103 °C and 111 °C. These activate the fan and the idiot light, respectively.


I could alter the resistor for the fan switch, to set it to come on sooner, perhaps 95 °C. This would be a trivial modification. I'll do the rest of this once finals are over next week.

[johnny]

patiently waiting...

j o

[wmax351]

Seems there are multiple versions of the relay.

The first one uses an "Automotive lamp monitor"
http://www.datasheetarchive.com/dlmain/Datasheets-111/DSAP0024225.pdf


The second one (and the post above) are from later bikes. The pic below of the new type is from a '92.

[subforry]

My soldering iron is at the ready and awaiting instructions.

[wmax351]

I'm going to get going on this. I might have the parts in hand (I will need a resistor, probably a fairly tight tolerance one).


My fan relay is out of the bike. I have a spare one from a spare harness too, so I will do both of them, If someone wants theirs modified, I can swap for my spare.


Both of mine are the later type. (with the single IC)


First step, I will map out the circuit, and figure out which resistor to modify.

[jenkinskg]

Could you just put a resistor in parallel with the temp sensor itself? or series not sure how it is wired
Which is the sensor that controls the fan, same as injection?

[wmax351]

That could work, however, it would also turn the overheat light on early.

[jenkinskg]

But then would cool down

[Inge K.]

Seems there are multiple versions of the relay.

The first one uses an "Automotive lamp monitor"
http://www.datasheetarchive.com/dlmain/Datasheets-111/DSAP0024225.pdf


The second one (and the post above) are from later bikes. The pic below of the new type is from a '92.

The relay in the first picture isn't the fan relay, but the BMU relay.

[wmax351]

Seems there are multiple versions of the relay.

The first one uses an "Automotive lamp monitor"
http://www.datasheetarchive.com/dlmain/Datasheets-111/DSAP0024225.pdf


The second one (and the post above) are from later bikes. The pic below of the new type is from a '92.

The relay in the first picture isn't the fan relay, but the BMU relay.

Good catch. Haha