I was in my garage filling, burping the cooling system.

So I had my gauge set to test mode 7, to display coolant temperature.

It uses the same sensor -gets its info from the ECM.

The fan is also controlled by the ECM.

It's supposed to click the fan on low speed at 105^C

I got it up to 107, and nothing. Took a long time to get that hot -which I think is good, but why didn't it turn on?

I've always assumed that it worked, because when I run the AC, the fan runs intermittently as it should -and I'm guessing this is when the AC Pressure reaches 8 bar. (AC has to run for only a few seconds to engage the fan)

From that time, it wasn't much more than a minute or two, and the temp dropped to around 90^C. I think that means cooling system is in good shape.

Why does my fan run when triggered by AC, but won't get triggered by coolant temp?

The low speed fan I believe runs constantly when the AC hits 8 bar. Check the resistor, very common problem.
I would recommend actually changing the resistor instead of the way the video fixed the problem but it is more work.

Okay, -Thanks for the video link.

So, yes, my low speed resistor reads Open.

So, that must mean that the intermittent fan I get with the AC is "the fan switches to high speed should the AC system pressure rise to 18 bar.". I'm guessing that must be around the pressure at which my AC compressor cycles on and off, hence the intermittences of the fan.

Anybody know where to get a resistor? I thought it only came with a new fan. -What about the specs of the resistor,... 14volt 15 or 30 amp should be enough (just need to double check the fuse value of the circuit). The big question is How many ohms?

The answers you need are in this thread
https://www.northamericanmotoring.co...-solution.html

I've found the cheapest place for the resistor is RockAuto if you are replacing the OEM resistor but there are other options like the video showed.

I installed the RA resistor about a year ago and it is still working perfectly. Hardest part of the job is getting to the resistor but def an easy Saturday job.

Other Options:
-0.330hm resistor fr mouser.com (PN:284-HS100)
-Dorman Resistor Kit
http://www.ebay.com/itm/170969660469?redirect=mobile-If you've the single plug harness, you may bypass that resistor (at your own risk).
Splice on fan side of the harness the red/green2.5mm & red/blue 4mm wires. Not the brown. Use at least a 12ga wire.

Radiator Fan wiring:
Brown=ground
Red/Blue4mm=hi speed
another Red/Green2.5mm=lo speed

Thanks for all the help. It is super appreciated. I just couldn't get my head past "....but the fan runs when I turn on AC". -So I never would have suspected (or checked) the resistor, even though I knew it was a common problem.

I think you saved me A LOT of time in trying to figure that out.

I found ECS has a resistor too. The repair I tried to do on my elbow/plastic tank connection leakes coolant already. I'll have to slide out the MFE to change the radiator anyway, so I'll just replace the resistor in its original location while I'm there.

Thanks again!!!!

Dorman's/Detroit Tuned ones might be the improved version. Doesn't have the same coil nor the green core. The stock type just won't last likely due to the heat in that area.

That's good to know.