Radiator Fan

I have a 97 Toyota Corolla and the problem I'm having is that my radiator fan is not working (I think)the reason I notice this is becuase I was getting a mix between heat and cold. I'll get heat and all of a sudden cold air will come in so what I did was replaced the thermostat and put everything back together and let the car run for about half an hour and found out the radiator fan was not working at all, but I started getting heat constantly without any problem. Next thing I did was run a wire from the battery directly into the the radiator fan and the fan works, so I know I'm good there. The next thing I did was replace the sensor the one on the water neck (coolant fan sensor) I believe that's what is call and still the radiator fan does not come on at all so now I don't know what other steps I should take in order to fix this problem,but I should mention that when I put my ac and put on heat the fan starts to work so don't know if this is suppost to happen. Now any idea of what the problem could be or where should I be looking since I already replace the thermostat and the coolant fan swicht sensor the one by the water neck thank you.

Check the fuse for the fan first. You should have two fan relays. One for the air conditioning fan and one for the normal fan. Try swapping relays if the fan works buy a new relay. The Ect sensor will be a two wire sensor. Make sure you replaced the correct one. If its bad try running with it disconnected the fan should run. If it runs buy the correct Ect sensor.

The fan is only going to turn on at a certain temp, it's winter!
Block the front grill with a piece of card board, so the engine cooling system can trigger the electric fan. 190f

During the summer, you can turn the Air cond cool max, and both fans should come on.

There is a cooling fan temperature switch (normally closed) mounted in the bottom of the radiator. It will kick the fan on when the temp gets to about 200°F. If you unplug that connector, the fan should come on and stay on. You can remove it and test it in a cup of hot water. It should be closed at room temp and open when in the hot water.

The ECT sensor on the water neck doesn't control the fans...it feeds the ECM the temperature info and gives the instrument cluster readout.

I have the opposite problem...

Both fans are always on.

1999 Prizm

Same sensor at bottom of radiator? Anyone have a photo, because this car was wrecked before I bought it and I think whoever changed the engine and did the core support repair forgot to hook it up? Not sure..

What wires lead to this sensor if it's not there so I can install one?

Courtesy of RockAuto:
http://info.rockauto.com/getimage/getimage.php?imagekey=488705&imageurl=http%3A//info.rockauto.com/BeckArnley/BA%25202011720-1.jpg

or

http://info.rockauto.com/getimage/getimage.php?imagekey=931212&imageurl=http%3A//info.rockauto.com/Airtex/SW653.jpg

Looks like a single connector going to it and is usually a normally closed switch. The wires leading to it typically come from the radiator fan relay, which if I'm not mistaken is located in one of the fuse and relay boxes in the engine bay. Check that too for a stuck relay. Finally, if it is a single conductor, that means the switch and the radiator must be grounded to the frame. If the ground is bad, then the switch will act as if it is open, making the fans stay on.

Hope this helps!