My 95 Civic Dx coupe is having overheating and cooling fan problems. I have noticed that the cooling fan has not been turning on recently.

These are the things I did:
1. I changed the thermostat, thermoswitch, & radiator cap.
2. I unplug the thermoswitch plug, I used a paper clip to close the circuit at the plug while the car key was at "on", and the cooling fan worked. So, I assume the fan, cooling fan relay & fuses work.
3. When the car is idling, there are pressure at both upper and lower radiator hoses, and both of them are warm/hot. So, I assume the thermostat and radiator cap are fine.
4. I thought the thermoswitch that I just changed was bad, so I bought another one. This is my second new thermoswitch in 2 weeks.
5. I noticed I have heat on when the I turn on the heater.

I noticed the coolant is boiling and leaking from the expansion tank. Cooling fan never on, even though I have been driving the car a while and the temp gauge is above the mid point.

Please help.... Why isn't the cooling fan on????