Most vehicles rely on a liquid-cooled cooling system to regulate their engine temperature. A mixture of water and antifreeze flows through channels and absorbs the heat produced by the engine. The heated liquid then moves to the radiator, which transfers the heat away from the coolant and into the air.
This system works best when the vehicle is moving, as it forces more air to go through the grille and into the radiator, enhancing its efficiency. But what happens if the car is just idling and is stationary? That’s where the cooling fan comes in. It helps move air through the radiator even if the vehicle is not in motion.
Most modern vehicles have electric fans that are controlled by relays, which are vital to keeping the engine cool. The relay controls the engine’s cooling fans as well as the fan for the A/C condenser. It also saves electricity.
Since excessive heat will damage the vehicle’s parts over time, a bad relay must be replaced as soon as possible.
Bad Cooling Fan Relay Symptoms
The relay is a critical part of a cooling system. When it malfunctions or breaks down, it affects the fan. The problem spreads to the rest of the cooling system, the engine, and the entire vehicle.
Fortunately, there are signs that warn the driver about a problematic relay. Keep a lookout for the following bad cooling fan relay symptoms:
The engine runs hot or overheats
Is the engine running hotter than usual? Is it overheating faster and without warning? The issue may stem from a malfunctioning cooling fan relay. Further, the heat issues often become noticeable when the vehicle is at rest.
However, a bad cooling fan relay isn’t the only culprit for excessively high engine temperatures. Many other issues can cause the engine to run hot or overheat.
The cooling fans don’t work
Rather than uncommonly high engine temps, the driver may notice that the cooling fans have stopped running. A faulty or broken relay cannot deliver power to the cooling fans. In turn, the unpowered fans won’t run, leaving the radiator to its own devices.
Deprived of the helpful influx of air from the cooling fans, the radiator cannot remove as much heat as it usually does. It sends still-hot coolant back to the engine, causing temperatures to rise as the coolant fails to do its job of cooling down the motor.
The cooling fans keep running
Conversely, the cooling fans may keep running even when the engine is offline. This odd behavior indicates a different issue in the relay that controls the fans.
An electrical short in the relay can lock the armature in its open position permanently. As a result, power will continue to flow to the electric motor, keeping the fans running continuously.
The vehicle’s battery provides power to electrical devices like the cooling fans. It only stores so much charge. If the fans run all the time, they will drain the battery faster than normal.
If the cooling fan relay has failed, you may see warnings, such as the check engine light and the temperature warning light, pop up on the dash.
Poor air conditioning performance
A faulty cooling fan relay can also negatively affect air conditioning (A/C) performance. The reason being, on most vehicles, is that the cooling fan doubles as a condenser fan. When the A/C is turned on, the fan moves air across the A/C condenser, thereby removing heat from the vapor refrigerant inside.
Possible Causes of a Bad Cooling Fan Relay
Cooling fan relays can stop working for any number of reasons. Common causes for relays going bad include:
- Overheating caused by the relay or a part mounted on or near the radiator
- Failure of the computer, temperature switch, or relay control module (i.e. the 1986 Ford integrated relay control module) that turns the relay on or off
- Damage caused by changing between circuits with different speeds and electrical load (i.e. fan relays on Chrysler LH models from the 1990s)
How to Tell if Cooling Fan Relay is Bad
There are several ways to tell if a bad cooling fan relay is to blame for an overheated engine. The easiest method is to start the engine and then turn on the air conditioning. If the fan doesn’t engage, there may be something wrong with the cooling fan relay.
Why? Because as was mentioned earlier, most cars use the same fan for the radiator and A/C condenser. There are, however, some models that use a dedicated second unit to the condenser.
In such a scenario, the condenser fan and radiator fan may or may not share the same relay.
If the cooling fan does not engage, you can check whether the relay is to blame by swapping it out for a different relay. Many automotive relays are similar in design, so you can simply take one from a different, noncritical system and insert it in place of the cooling fan relay.
You’ll know the cooling system relay is faulty if the fan works with the substitute relay.
You can also measure the relay coil’s resistance. A normal relay’s resistance will read between 40 to 80 ohms. Higher resistance levels warn that the coil has started to fail while lower readings mean the relay has broken down.
Still another DIY test involves shaking the cooling fan relay and listening for any noises. A broken armature will rattle around the relay.
What Does a Cooling Fan Relay Do?
The cooling fan relay is an electromagnetic switch that controls the power supply to the engine’s cooling fans. It ensures that the energy-intensive devices only run when needed, usually when the vehicle is immobile.
When the engine temperature approaches unsafe levels, the vehicle’s computer or temperature switch turns on the cooling fan relay. The activated relay completes a circuit, allowing an electric current to flow through it and reach the cooling fans.
Different Types of Cooling Fan Relays
There are several types of cooling fan relays. Their main difference involves the winding armature that they use to complete an electrical circuit.
Normally open relay
The most common type of relay uses an open armature. When the relay coil gets energized, the armature closes. The completed circuit allows the current to flow to the fan motor.
Normally closed relay
The opposite of the normally open relay, this type uses a closed armature. Energizing the relay coil opens the armature and completes the circuit.
This relay type uses two circuits, one of which employs an open armature while the other one has a closed armature. Thanks to its use of both armatures, a dual relay can conduct an electric current in both open and closed positions.