Hopefully, this problem was addressed before. Our 93 Paseo's main cooling fan runs continuously. Does not matter if the AC switch is on or not (system has a slow freon leak so is not fully charged, if that matters)
I have checked or replaced the following: the fan relays and temperature sensor sending unit on the t'stat housing.
I would check the temp sensor in the radiator but cannot seem to locate it or the wire(s) that connect to it. I have read the AC amplifier could be the culprit but am not happy about its location under the dash. The only way to override the unit is to disconnect the motor wiring at the coupler. Has anyone else had this problem? What am I overlooking? Have owned a Cressida in the past and know Toyota likes to over-engineer their cars with things the normal mechanic would never think of.
Thanks for any valuable assistance.

In my 1993 Toyota Starlet that problem Ocurred six months ago. (Note that these cars are very similar in A/C, Radiator, cooling system, etc.)

The Air Conditioner has a Filter-Dryer in the high pressure side (The tube that comes from the condenser in the front of the car passes to this filter and then to the Evaporator in the interior of the car.

THIS FILTER has a little sensor (in my car the filter is located in the front behind the bumper)and this sensor tends to stay open because is old and need changing.

In normal operation this device opens the circuit only when you tun on the a/c and the pressure/temperature is too high at the refrigerant that comes out the filter to the evaporator. When the sensor opens the circuit, the fan relay closes the fan circuit and turns on the fan.

With the sensor working properly, if you turn on the a/c on a cold or fresh day or in a highway, the fans turns on but slowly (in series) because the temp. or pressure of the refrigerant is not too high and doesn't need too much air flow.

This sensor looks like the oil pressure sensor but have a different plug, with 2 wires.

HOW I SOLVED THE PROBLEM?
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NOTE: I have some mechanical experience about this car but I don't warranty this will fix your sensor. if doesn't work for you, you may need to replace it by a new one.
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1. First check the relays are in place and the water temp. sensor is plugged in.
2. If you see the a/c sensor, on the filter/dryer or in the piping that comes from the filter to the interior of the car (the thinner of the two aluminum pipes) disconnect the sensor's plug. (The car's key switch must be in ON possition but with the engine and a/c off). Clean the contacts with contact cleaner and plug it back. If the fan doesn't turn off, then go to the next step.
3. Put a piece of thin wire between the two terminals of the plug to close the circuit. IF THE FAN TURNS OFF, NOW YOU KNOW THE SENSOR IS BAD!
4. Here is the part I said that worked for my car. You have to check the Refrigerant/Freon level. If good or if your car's a/c works good, you have to drive your car for 2 to 5 days with the a/c on highest level and with the piece of wire between the contacts of the sensor instead of connecting to the sensor. The over pressure or temp of the freon fixes the sensor that could be stuck or slightly corroded in its interior. If you drive the car in the city and with high ambient temperatures works best. Don't worry your car will not overheat because the water temp sensor also opens this circuit and the relay turns on the fan.
5. After a few days, detach the piece of wire and plug the sensor.
6. If the car is cool (temp. below half) and when you turn it on the fan stays off, you have "FIXED" your sensor but you have to turn on the a/c on highest level with the windows open to check if the fan turns on after few seconds. (NOTE: Time may vary. if the outside temp is too cool maybe it never turns on, but at noon in a hot day could turn on in ten seconds approximately. You also can help it to turn on by keeping the car at high idle for a while (eg. at 2000-2500rpm for 30 seconds to 1 minute with the a/c on high).
7. If want to ask me more, write to me: javierbobea@yahoo.com

Just curious, do you work with cars regularly? You seem to have alot of knowledge on such a complex situation! Thanks for the tips, this happened with a nissan I am still bangin' around!