ELECTROVENTILADOR DIESEL 1.9 Model 2009

Hi!
I have a problem with my truck; the radiator fan never turns on. The only way it comes on is by turning on the air conditioning. I've replaced the thermostat, but it's still the same. In the thermostat housing, there are two sensors: a green one with two contacts and a blue one with four contacts. If I disconnect the blue sensor with the engine running, both radiator fans turn on at full speed. As an additional detail, there's oil in the coolant. Does anyone know how to fix the radiator fan issue first?
Thanks a lot.

If I were you, I'd first check for oil in the coolant.
It could be due to a problem with the gasket.
And if I'm not mistaken, the electric fan is activated by a temperature sensor located on the radiator.
Perhaps the sensor got oily, which is why it's not working.
Best of luck, and check the oil problem.

Thanks for your reply, Guillermo.
From what I've seen and been able to find out, the radiator doesn't have a temperature sensor. In the water box where the thermostat is located, there are two sensors: a green one for the coolant/engine temperature and a blue one that controls the two electric fans and the temperature gauge on the dashboard. Between the two electric fans, above them, there's a box with three relays, which I tested and they're working fine. So far, I haven't found the cause of the problem.

But did you check the one that activates the fans?
Is it a sensor or a thermoswitch?

The last case I had of that type was a problem with the wiring; a faulty connector. I hope this helps.