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Did you have it checked for DTC'S - diagnostic trouble codes ? The cooling fans are controlled by the PCM - engine computer , with the use of three relays ,located in the under hood electrical center . Do you know how to do electrical testing ? Relay Driven Dual Cooling Fan Diagnostics Looking at wiring diagrams i don't see any connection between the brakes an cooling fans . Checking for DTC'S an doing electrical testing of control circuits from the PCM , Power circuits from the fuse / relay box . Checking grounds an pulling relays ,check for corrosion .
Either the temp sensor is bad, or the relay is bad. or the fan motor is bad. Or you have a blown fuse. Look for fuse first.... To test if fan motor is bad disconnect the connector to the fan and jumper it to the battery.if it spins it's good. the other two. use a component locator to find their location and replace. they are inexpensive. Temp sensor is in the cooling circuit (radiator...maybe next to thermostat) the relay will be in a fuse box under the hood.
The radiator cooling fan on your 1990 Ford Thunderbird Super-Coupe is supplied power via the BLACK, 18 Gauge, fusible link near the battery. If your cooling fan is not getting any power to operate (and you are certain that the fan motor is in good working order) the most likely cause of you fan not working is a failure in the Constant Control Relay Module (CCRM), which is mounted to the upper radiator support.
I have replaced many of these because the circuit boards inside them like to burn.
HERE IS HOW TO TEST IT:
Check for power at the CCRM on pins 3 and 4 BLACK/ORANGE wires. If there is power there, the fusible link is good. If there is no power at these connectors, repair the fusible link or the circuit between the fusible link and the CCRM.
Then, the Powertrain Control Module (PCM) turns the fan on by grounding the fan relays inside the CCRM at Pins 14 and 17.
So if you have power on the BLACK ORANGE wires, You should be able to manually turn the fan on by grounding Pin 14 (TAN/ORANGE) for fan LOW speed and Pin 17 (GREEN/PURPLE) for fan HIGH speed.
If grounding these wires does not get the power to come on at the fan motor, then the CCRM needs to be replaced.
If this makes the power come on (at the motor connector) but the motor will not run, then you need to replace the fan motor.
If grounding these wires makes the motor run, you have a problem with the engine coolant temperature sensor or the PCM.
The car model was not included in the question. In general if the radiator fan is not starting the first thing to check are the fuses. Depending on the car's model there is one or two fuses in line with the cooling fan circuit. If there are two fuses, then one is in the fuse plate inside the car, the other one is under the hood.
The next part to test is the thermostat. The thermostat housing is located on the refrigerant fluid lines, either near to the radiator, or near to the engine block. The thermostat can be tested using VOM tool. Read either Ohms or volts to find out if the thermostat is closing the fan circuit when the engine is hot.
Most fan circuits use also relay. Variable speed fans have often more than one relay. The fan relay(s) is often located under the hood. Relays can be tested reading volts at their contacts or swapping the relay with one of the same kind.
If fuses, relay and thermostat are OK, then the fan motor is often the next test. The motor can be tested energizing it directly. Variable speed fans have more than two wires powering the motor. To avoid risk of damaging the fan motor the repairer should refer to specific wiring diagrams before jumping fan cables. A different way of testing the motor is reading volts at fan motor while engine is hot. If there is volts at motor contacts but motor does not come on, then the fan motor is defective.
if the fan still works on highest setting only the fan speed resistor block is faulty.
if the fan doesnt work on highest setting check for power at fan while on highest setting with globe test light, as well as checking fuse for fan. 2 wires one power other is earth. if power is there the fan motor needs replacing so long as the earth wire is also ok check with voltmeter on Ohms for continuity should be a couple of Ohms any higher is no good.
Which fan motor do you want to repair, the one inside the car for climate control or outside for engine cooling next to radiator? Inside locate fan please note some libraries have repair manuals that you can check with them for free you usually can go and find at least the location this way. Check fuse location and electrically check BOTH SIDES of the fuse with a digital volt meter not a test light some circuits in newer computer control vehicles can be damaged by test lights. Once you find the fan (inside) it also has a resister pack usually somewhere on the a/c heater assembly, check for voltage at the input of the motor AND the ground side also remember electricity needs a complete circuit. If outside cooling motor look for a fuse box outside in the engine compartment and check that also inspect the wiring connections in line for melting usually at the motor this is a tell tale sign that the motor is using too much current. Also there needs to be a temperature switch in the cooling system sometimes in the radiator or in the engine/block/head. watch the color code of the wire from motor trace back usually to a relay or two speed resister block. Also some cars have a secondary fan for the A/C condenser I assume you don't mean this one.
1. check the cooling fan fuses
2. supply battery voltage directly to the fan assembly plug
a. if fan is good
locate and test/replace cooling fan relay
b. if bad
replace cooling fan assembly
if still is not working check continuity cooling fan system circuit/wiring
Above is the diagram for a 4 cylinder. It appears that you might have a fusible link which looks like a regular wire instead of a regular fuse. If you have A/C on your car you can turn it on and this automatically should turn the cooling fan on. If I remember correctly these cars have problems with the Coolant temperature sensor located near the thermostat. It will have one yellow wire going to it. You can also try to swap the cooling fan relay with the horn relay or another relay that looks similar under the fuse block. There should be a diagram of the fuses and relays under the cover. Try with the engine off and key out try to turn the fan by hand. If it does not move freely the cooling fan motor is bad. Other than that you will have to bring to a shop to have the circuits tested... Good luck.