I live in the southwest where it gets HOT in the summer. I would like to be able to manually turn on the cooling fan in stop-and-go traffic when the engine really warms up. Based on this schemayic from 2007, the ECM grounds the negative side of the relay which closes the contacts to the fan.
If I install an ON-OFF switch that would ground the dark green wire, the fan should come on with no electrical issue with the ECM. Am I right? Opinion?
A push button switch could easily be mounted in the small compartment in front of the shifter.


Ground the dark green wire and the fan will run.

 

Looks like you will just short out the relay possibly the ECM

 

I'm guessing there is a good chance that would work, but using a DPST switch will allow you to isolate the switch from the ECM when you turn on the fan. Alternatively, just add a second fan relay in parallel and connect your switch to that.

 

If it’s that “HOT in the summer “ then you must be using the AC. If you’re using the AC then the cooling fan will be on.
So I’ll ask. Why the need to put in a switch ?

 

I think you’d be better off inspecting the radiator fan make sure all the fan blades are intact, the plastic has been known to fail and blades break off. So if you do turn on the fan manually it still won’t move air to cool the radiator coolant

 

What do you think iis overheated?
The fan is always on when the AC compressor is on. It turns on at about 219F and back off at 179F when the compressor is not on. A manual switch will do nothing but cause problems, the temp MUST be above 179F. If it gets and stays above 220F your problem is that the fan is not working as designed or there are other problems.

 

This would not short the relay, it would ground the negative side of the coil in the relay just like the ECM does (using a transistor). By grounding this wire the coil would be energized and close the contacts, which would start the fan motor.
Fuel injectors work the same way, the ECM grounds the negative side of the injector to open the nozzle.
This should not damage the ECM, in my opinion. Think of it as a parallel switch controling the same device.

 

I want to be able to control the fan without the A/C being turned on. The engine does not overheat, the fan comes on at 217 like it is designed to, I would like to be able to start the fan at around 200 instead. Get a head start on the cooling in city driving.

 

Correct me if I am wrong, but I believe the fan turns off at a certain speed, for example 35 MPH. There is a point where forward movement of the car produces convection currents that exceed the fan's capacity, so the fan isn't needed.

 

I’m not sure about the fan not required above 35 mph , it’s plausible but I can’t confirm that.