* Engine coolant temperature: This is the primary reason. When the engine coolant reaches a pre-determined temperature (usually around the 212°F/100°C mark), a sensor signals the engine control unit (ECU) or a dedicated fan control module to activate the fan. This is crucial to prevent overheating.
* Air conditioning operation: In many vehicles, including some 1991 Scoupés, the A/C system will also activate the radiator fan to help cool the refrigerant condenser. Even if the engine isn't particularly hot, the fan may run when the A/C is on.
* Low coolant level (sometimes): Some systems incorporate a low-coolant level sensor that can trigger the fan as a warning indicator. However, this is less common than temperature-based activation.
* Faulty fan control module/ECU: A malfunctioning control module (either a dedicated fan module or the ECU itself, depending on the car's setup) can cause the fan to run constantly or intermittently, even when the engine is cold.
* Faulty temperature sensor: A faulty coolant temperature sensor can provide incorrect readings to the control module, leading to the fan running unnecessarily or failing to run when it should.
* Short circuit: A short circuit in the wiring harness leading to the fan or the fan itself can cause it to run continuously.
Troubleshooting:
If your Scoupe's radiator fan is running constantly or incorrectly, you'll need to diagnose the problem. Here's a basic approach:
1. Check coolant temperature: Is the engine overheating? Feel the radiator hoses – are they excessively hot?
2. Check A/C operation: Turn off the A/C. Does the fan still run? If it stops, the A/C system is the likely cause.
3. Inspect the fan relay: Locate the relay (a small square component often found in the fuse box under the hood or dashboard) and check if it's clicking or sticking.
4. Check the coolant temperature sensor: This sensor often has two wires connected to it. You might need a multimeter to check its resistance at different temperatures (consult a repair manual for specifications).
5. Check wiring and connections: Inspect the wiring harness for any damaged, frayed, or loose wires, especially near the fan and sensor connections.
If you are not comfortable working on car electrical systems yourself, it's best to take your car to a qualified mechanic for diagnosis and repair. Incorrect diagnosis could lead to further damage.
