I replaced the Radiator Fan Switch, and checked the coolant fan fuse in Aux Relay Panel 2. However the problem still persists: the coolant fans just wouldn't turn on. However when I turn on the A/C, then they do come on alright. Still, it is not sufficient to prevent them from overheating.

Thanks for all the help. What should I do now?

1. How could the fan relays (1 and 2 in Aux Relay panel 1) be tested? Can I short to see if the fan works?

2. Where is the fan resistor?

Pull back the rubber insulation on the back of the plug. You should find a brown wire.

Turn the ignition switch on.
Insert a bent paperclip into the plug socket where the brown wire is connected and bridge it to one of the other sockets.

The brown and white wire will give low speed fan and the brown and blue high speed.

Remember the engine needs to be pretty hot to activate the fan normally and the high speed is more like an emergency system which should only activate under extreme conditions.

I did this job yesterday and when testing I had to let the car idle for a least 20 minutes before the fan activated.

THanks, that was very useful information. I did exactly as you told and saw that both the low speed and high speed worked fine. This leads me to think that the problem could be with the thermoswitch, but I had replaced it with a new one only yesterday. So now I am confused: seems like the relays are fine, seems like the coolant fan fuse is fine, and the thermoswitch is brand new, but still the fans don't work nevertheless.

Any suggestions? Could it be the air problem I read somewhere else? How can I see if there is trapped air? One more thing: the driver-side hose (upper) into the radiator gets VERY hot, but the lower passenger-side hose remains cold even when the engine is overheating. The thermostat had been recently replaced, and also it seems the coolant does circulate, as the car runs fine when I run with the cabin heat at max (well it effectively cooks me when driving, but the car runs nevertheless)

Thanks

Or incorrectly installed.
I'm not sure if you can do it on this engine but I have seen a thermostat installed back to front.

The passenger side hose should also get hot.

If you study the diagram on this link you will see why you still get cabin heat.<ul><li><a href="http://www.12v.org/engine/index.php?section=cl&amp;view=cool">Coolant circulation diagram</a></li></ul>