2008 Tundra Blower Fan

The old fan has 12v feed, ground and pwm signal. With external power and ground connected i took and applied the ground to the signal and it would run for a sec on high and would shut off. The new one did nothing so i knew one or the other is bad. I tried applying voltage or ground on the signal but nothing would happen. Does it require the pulsed voltage to ground to make it run? The harness side of the signal wire read 0 with dvom. I'm sure a scope is needed to see the signal. The original fan was bad but I'd like to know what does it take to signal the fan or fet inside the fan.

Hey Xbin, I'm wondering if you got a bad new fan module? :huh:

If you're willing, I'd suggest cutting the light green signal wire close to the fan, somewhere easily repairable later. This'll allow you to test the fan module independent of the A/C Amplifier and it's wiring.

With the wire clipped, you *should* get a flat 5V on the fan side of that light green wire. These variable fan systems almost always have the fan module provide a voltage, and the controller pulses it to ground more and more to kick up the fan speed. If you find that 5V, then that'd suggest at least part of the transistor is OK. If you don't find that 5V, and the power and ground to the fan is good, then that's a bad fan module.

If you find the 5V, you can temporarily reconnect the light green wire and observe the duty cycle on a DVOM while varying fan speed. You may not be able to see the signal like on a scope, but seeing duty cycle changes strongly suggests the A/C Amplifier control circuit is OK. Seeing no changes would point towards the A/C Amplifer or an open wire.

opel astra

The old fan was bad and the new one worked. I got nothing on the green wire harness side with a dvom on all settings. I was just curious of what it took to make it run with external power and ground outside of the vehicle. If one supplied 12v power and ground and. 5v to the control of the fan i would think it would run on high. One really needs a scope nowadays.

Ah OK, I understand. Really, what you were doing by supplying power and ground and grounding the signal was the right way to do it. A flat 5V will result in no operation.

I'm not sure why it ran for a second then quit? Maybe a connection moved when the fan spun up and shifted around?