Electrical Electric fans came on with car off...like a ghost

[Mstng93SSP]

I have contour fans with a Derale DER-16795 controller. It has been on the car 2 years+. Today, out in the garage, not touching the car, no key in the car, have not driven the car since yesterday, and all of a sudden the electric fan came on at 100%. They would not stop. Had to disconnect the battery. I think the controller is fried. Anyone ever have this happen?

 

[AeroCoupe]

You are no dummy so I’m going to assume that on the controller you wired it correctly which would make me say it’s toast. As long as you provided the controller with adequately sized power and ground wires and none of the wiring got cut / chafed then stuff happens.

 

[Mstng93SSP]

Yeah, was working perfect for two years. Gonna pull the cover and take a look inside.

 

[Mstng93SSP]

Inside of the controller looked ok. It did it again, came on with the car off. I unplugged the sensor wire for the sensor that is on the radiator and the fans shut off. This seems strange as if I remember correctly there is no 12v power on the sensor.

 

[Mstng93SSP]

But thinking about it now, the fan does run for 1 minute or so after the car is shut off. Maybe the sensor is bad?

 

[KRUISR]

I would vote for bad sensor. How is the sensor configured? I have an Audi/VW sensor. It has 3 wires, 12V in and then low speed out and high speed out once temps are made. Some sensors are a ground, when temp is made it completes the ground circuit to power fans. If using the latter type, that would explain what you are seeing. The sensor failing closed and ground circuit is completed.

Depends how system is wired.

 

[nickyb]

Sounds like you found the problem.

 

[KRUISR]

But thinking about it now, the fan does run for 1 minute or so after the car is shut off. Maybe the sensor is bad?

The fan running after the car is off would be because coolant is still above trigger temp of the sensor and it takes a minute or so to cool it down. Your fans and control system are powered directly from battery power, not key-on power. Mine does the same thing - I have Contour wiring and control system with a VW sensor - if I shut car off when fans are running, they will continue to run for a minute or two until sensor gets cool coolant and shuts down. My sensor is in lower rad hose.

 

[Mstng93SSP]

Thanks for the input. I appreciate it. I ordered a new sensor.

 

[Noobz347]

 

[AeroCoupe]

I am not familiar with this controller so I did some reading and am impressed with it. That doesn’t mean a lot as I’m not a controller guru but I’ve been around a few of them and for me it’s a quality piece. Found the install instructions and if you scroll down to page four and they describe how to test the sensor.

https://derale.com/product-footer/product-instructions-footer?download=3532:16795-pwm-electric-fan-controller&start=260

 

[Blown88GT]

The Derale Controller is a DCC Controller design. He held the patent & licenses it to Derale.
https://patents.google.com/patent/US7006762B2/en

https://patents.justia.com/inventor/brian-l-baskin