How Do You Wire an Electric Fan Relay Step by Step?
When it comes to maintaining or upgrading your vehicle’s cooling system, understanding how to wire an electric fan relay is an essential skill. Whether you’re aiming to improve engine efficiency, prevent overheating, or simply replace a faulty component, mastering the basics of electric fan relay wiring can save you time and money. This seemingly small but crucial part plays a pivotal role in controlling the electric fan’s operation, ensuring your engine stays at the optimal temperature under various driving conditions.
Wiring an electric fan relay might sound intimidating at first, especially if you’re new to automotive electrical systems. However, with a clear understanding of the relay’s function and the proper wiring techniques, the process becomes much more approachable. The relay acts as a switch that allows a low-current circuit to control a high-current fan motor, protecting your vehicle’s electrical system from overload and enhancing overall reliability.
In the following sections, you’ll discover the fundamental concepts behind electric fan relays, the tools and materials needed, and the step-by-step process to wire one correctly. Whether you’re a seasoned DIY enthusiast or a beginner eager to learn, this guide will equip you with the knowledge to confidently tackle your electric fan relay wiring project.
Wiring the Electric Fan Relay
Wiring an electric fan relay correctly is critical to ensure reliable operation and to protect your vehicle’s electrical system. The relay acts as a switch that allows a low-current circuit to control a high-current fan motor, preventing damage to the switch or control module.
Begin by identifying the four primary terminals on a standard automotive relay:
- 85: Relay coil ground
- 86: Relay coil positive (trigger input)
- 30: Common terminal (power input)
- 87: Normally open terminal (power output to the fan)
The relay wiring involves connecting these terminals to the appropriate components: the battery or fuse block, the electric fan, the fan switch or temperature sensor, and ground.
Step-by-Step Wiring Instructions
- Connect Terminal 30 to a fused 12V power source. This is typically from the battery positive terminal or a fuse panel capable of supplying the fan’s current. Use an inline fuse rated slightly above the fan’s maximum current to protect the wiring and relay.
- Attach Terminal 87 to the positive lead of the electric fan motor. This terminal will provide power to the fan when the relay is activated.
- Ground the fan motor’s negative lead to chassis ground. Ensure the grounding point is clean and free of paint or corrosion to guarantee a solid connection.
- Connect Terminal 85 to a reliable chassis ground. This completes the relay coil’s circuit.
- Wire Terminal 86 to the fan control switch or temperature sensor output. When this switch closes or the sensor signals, it sends 12V to this terminal, energizing the relay coil and allowing current to flow from Terminal 30 to Terminal 87.
Relay Wiring Diagram and Connections
| Relay Terminal | Connection | Function |
|---|---|---|
| 30 | Fused 12V battery supply | Power input to relay |
| 87 | Electric fan positive lead | Switched power output to fan |
| 85 | Chassis ground | Relay coil ground |
| 86 | Fan switch or temperature sensor output | Relay coil positive trigger |
Additional Wiring Considerations
When wiring the relay, consider the following to enhance durability and safety:
- Use appropriate wire gauge. The wires powering the fan (terminals 30 and 87) should be sized to handle the maximum current draw of the fan, typically 12-14 gauge wire. The coil wires (terminals 85 and 86) carry minimal current and can be 16-18 gauge.
- Incorporate an inline fuse or fuse holder. Protect the power wire feeding terminal 30 with a fuse rated slightly above the fan’s maximum current to prevent wiring damage in case of a short circuit.
- Secure all connections. Use solder or high-quality crimp connectors to ensure reliable electrical contact, and protect connections from moisture and vibration with heat shrink tubing or electrical tape.
- Route wiring away from heat sources and moving parts. This prolongs wire life and reduces the risk of damage.
- Test the relay operation before finalizing the installation. Verify that the fan turns on when the control switch or sensor is activated and turns off when deactivated.
Integrating the Relay With a Temperature Sensor or Switch
The relay coil (terminals 85 and 86) is energized by the fan control circuit, which often involves a temperature sensor or a manual switch. This integration allows the fan to operate automatically based on engine temperature or user control.
- A temperature sensor switch typically closes the circuit at a preset temperature (e.g., 195°F), sending 12V to terminal 86 and activating the relay.
- A manual override switch can be wired in series or parallel with the temperature sensor to allow the driver to turn the fan on or off as needed.
It is essential that the sensor or switch circuit is properly fused and uses appropriate wiring to prevent damage or electrical faults.
Common Relay Wiring Configurations
Below is a summary of typical configurations used with electric fan relays:
| Configuration | Description | Typical Application |
|---|---|---|
| Single Relay with Temperature Sensor | Relay coil energized by a temperature-activated switch | Automatic fan control based on engine temperature |
| Relay with Manual Override Switch | Manual switch wired in parallel to the temperature sensor | Allows user control in addition to automatic operation |
| Dual Relay Setup | Two relays controlling high and low speed fan operation | Variable fan speed control for better temperature management |
Understanding the Components of an Electric Fan Relay Wiring System
Before wiring an electric fan relay, it is essential to understand the primary components involved and their functions:
- Electric Fan: Responsible for cooling by circulating air through the radiator or engine compartment.
- Relay: An electrically operated switch that enables a low-current circuit to control a higher-current load safely.
- Power Source: Typically the vehicle’s battery or a fused ignition feed.
- Ground Connection: Completes the electrical circuit by providing a return path.
- Control Switch or Signal: Activates the relay coil, often connected to the thermostat, temperature sensor, or manual switch.
A standard automotive relay will usually have four or five terminals, identified by their numbers:
| Terminal Number | Typical Function |
|---|---|
| 30 | Battery power input |
| 87 | Power output to the fan |
| 85 | Relay coil ground |
| 86 | Relay coil positive input |
| 87a | Normally closed contact (optional) |
Understanding these terminals is crucial for proper wiring and avoiding damage to components or circuits.
Step-by-Step Guide to Wiring an Electric Fan Relay
Wiring an electric fan relay involves connecting the relay terminals correctly to the power source, fan, and control switch. Follow these steps carefully:
- Identify Relay Terminals
Locate the relay terminals 30, 85, 86, and 87 on your relay, either by printed numbers or a diagram.
- Connect Terminal 30 to Power Source
- Use a fused wire (typically 15-20A fuse) connected directly to the positive terminal of the battery or a reliable fused power source.
- This ensures the relay receives constant power safely.
- Connect Terminal 87 to the Electric Fan
- Run a wire from terminal 87 to the positive input terminal of the electric fan motor.
- This wire will supply power to the fan when the relay is activated.
- Ground the Electric Fan
- Connect the fan’s negative terminal to a good chassis ground or battery negative terminal to complete the fan’s circuit.
- Connect Terminal 85 to Ground
- Attach terminal 85 on the relay to a clean, secure ground point on the vehicle chassis.
- This is necessary for completing the relay coil circuit.
- Connect Terminal 86 to Control Signal
- Connect terminal 86 to the control switch output, which could be a thermostat switch, temperature sensor, or manual override switch.
- This wire provides the relay coil with the positive voltage needed to energize the relay.
- Test the Circuit
- After all connections are made, test the system by activating the control switch or reaching the temperature threshold.
- The relay should click, and the fan should turn on. If it doesn’t, recheck connections and fuse integrity.
Additional Wiring Tips and Safety Precautions
- Use Correct Wire Gauges:
- Use at least 14 or 16 AWG wire for power and fan connections to handle the current safely.
- Use smaller gauge wire (18-20 AWG) for the relay coil circuit.
- Install a Fuse Close to the Power Source:
- Always place a fuse within 12 inches of the battery or power source on the relay’s terminal 30 wire to protect against short circuits.
- Secure All Connections:
- Use soldered joints or quality crimp connectors to ensure stable, corrosion-resistant connections.
- Avoid Routing Wires Near Heat or Moving Parts:
- Route wiring away from exhaust manifolds, sharp edges, and areas where wires may be pinched or worn.
- Verify Relay Coil Voltage:
- Ensure the relay coil voltage rating matches your vehicle’s electrical system (commonly 12V).
- Test Before Final Assembly:
- Temporarily secure wires and test the fan operation before permanently mounting the relay and fan.
Common Relay Wiring Configurations for Electric Fans
Different applications may require slight variations in wiring. Below is a comparison of typical relay wiring setups:
| Configuration | Description | When to Use |
|---|---|---|
| Thermostat-Controlled | Relay coil triggered by a temperature switch | Automatic fan operation based on engine temp |
| Manual Switch Control | Relay coil connected to a manual on/off switch | Driver-controlled fan activation |
| ECU-Controlled | Relay coil triggered by Engine Control Unit output | Modern vehicles with computer-controlled fans |
| Dual Relay Setup | Two relays for low and high fan speeds | Vehicles with multi-speed electric fans |
Each setup requires the same basic relay wiring principles but varies in the source of the control signal at terminal 86.
Troubleshooting Common Wiring Issues
| Symptom | Possible Cause | Recommended Action |
|---|---|---|
| Fan does not turn on | No power to relay terminal 30 | Check fuse, battery connection, and wiring |
| Relay clicks but fan doesn’t run | Fan ground not connected or fan motor faulty | Verify fan ground and test fan motor directly |
| Relay does not click | No signal at terminal 86 or bad ground at 85 | Check control switch, wiring, and ground points |
| Relay stays on continuously | Stuck control switch or relay contacts welded | Inspect control switch and replace relay if needed |
| Intermittent fan operation | Loose connections or faulty relay | Tighten connections and test relay functionality |
Proper diagnosis ensures safe and reliable operation of the electric fan system.