Home | Engine | Radiator Fan Not Working When Is AC On {SOLVED}

Radiator Fan Not Working When Is AC On {SOLVED}

February 11, 2024 | Victor Lukasso

The Radiator fan is a crucial component of a car’s cooling system that helps prevent engine overheating by dissipating heat from the engine.

Therefore, when the radiator fan becomes faulty, the engine stops working at its optimal temperature, and this may cause damage to several engine components if not addressed on time.

And for this reason, it’s advised that you take action once you notice that your radiator fan fails to operate when the AC is turned on.

In this article, we’ll briefly explain how the radiator fan works and the possible causes behind a radiator fan not working when the AC is on, with troubleshooting steps to resolve the trouble.


How the Radiator Fan Works

When you crank your engine for the first time, the fan doesn’t start blowing air immediately. Instead, it waits for the engine to reach its operating temperature.

The time it takes for an engine to reach its optimal temperature may differ, but it is usually between 5 to 20 minutes. However, you can speed this up by increasing the load on the engine.

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For example, turning on the air conditioner will automatically cause the fan to start working.

But what do you do in abnormal cases where the fan doesn’t blow even after the AC is turned on or the car has attained its operating temperature?

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Continue reading…

Should the radiator fan turn on when AC is on?

By default, the radiator fan is supposed to turn on whenever the AC is on because of the load it exerts on the engine.

If the fan doesn’t turn on, you should check for a blown fuse or relay, damaged wiring, bad temperature sensors, or the wiring harness of the radiator fan.

Radiator fan not turning on When AC is ON – Causes

Here are some factors that may contribute to a radiator fan not working correctly when the air conditioner is turned on.

A Blown Fuse or Relay

If a fuse or relay associated with the fan blows, this can lead to fan failure because it disrupts the electrical flow in the cooling system.

The function of the fuse is to protect components from electrical surges. Meanwhile, the relay helps regulate the amount of electricity in the system.

Low or zero coolant

Another possible reason the radiator fan wouldn’t turn when the AC is on is insufficient coolant in the reservoir.

This is so because temperature sensors can’t read the hotness of the engine directly. Instead, they use the hotness of the engine coolant to tell the engine temperature.

Faulty Temperature Sensor

The PCM relies on sensors to oversee the well-being of all vehicle components. One is the coolant temperature sensor that monitors the engine’s heat levels and triggers the fan’s operation.

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If the temperature sensor goes bad or sends incorrect signals, the fan may not turn on whenever the AC is switched on, resulting in improper cooling.

Wiring troubles

Wear and tear, incorrect installation, or damage to the wiring harness of the radiator fan can result in loose wiring comments that may prevent adequate power supply.

You can visually inspect the wiring connection for any breaks or damage and resolve them immediately.

Radiator Fan Issues

Electric motors power the movement of the radiator fan; when the fan doesn’t respond when the AC is plugged in, you should check the fan itself.

A Bad Fan Controller Module

Some car manufacturers install fan control modules in the engine bay and are responsible for regulating the cooling fan.

However, this component is susceptible to damage due to heat from the engine compartment, corrosion, or other vehicle-specific issues.

In addition, a faulty AC high-pressure sensor can also cause the fan not to respond when the AC is turned on. You can have the high-pressure sensor cleaned or replaced depending on its state.

How to Fix Radiator Fan Not Working When Is AC On

If your radiator fan fails to run while the air conditioner is turned on, follow these steps to diagnose and repair the problem:

Replace the Damaged Cooling fan

Once you’re sure the problem is from a faulty cooling fan, you can replace it or change individual damaged components.

For example, you can decide to change just the blade, but the issue is usually from the motor, which requires you to get a complete set of cooling fans.

Replace Blown Fuses and Relay

The radiator fan usually works with a 50 Amp fuse and a relay which can be found in the fuse box. You can use a multimeter to check the continuity of the fuse and replace them with new ones.

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Additionally, you can swap the fan relay on your vehicle with a similar one from another system to see if that resolves the problem.

If it does, you’ll need to replace the relay immediately.

Check the Coolant Level

Ensuring that the level of the coolant in the reservoir isn’t below the gauge is a way to get rid of this trouble. This also aids the sensors in reading the correct engine temperature.

Check the Temperature Sensor

Another thing to consider is the temperature sensors. The sensors will send incorrect readings to the PCM if they go wrong.

If this is the case, then you may need to get the coolant temperature sensor replaced.

Replace the Damaged Control Module

If the control module is faulty, the fan will not work whether the AC is on or not, making it more detrimental to your car’s health.

You can have it replaced to save you the risk of costly repairs.

Repair Damaged Wirings

Examine the wiring harness attached to the fan motor carefully to ensure no loose or damaged wires. As needed, repair or replace any damaged wiring.

Consult a Mechanic

If none of the above tips could help you resolve the trouble, you may consider taking your vehicle to a mechanic.


Will car AC work without a radiator fan?

Yes, but it can cause overheating and lead to potential engine troubles. The AC and radiator fan are supposed to work hand in hand to keep the system cool by blowing off heat.

Why is my radiator fan not turning on with the AC?

If your radiator fan stops working, it’s probably because of a faulty relay, fuse, low coolant level, or damaged wiring connection.

What sensor turns on the radiator fan?

The coolant temperature sensor is the sensor in charge of turning on the radiator fan. It estimates the engine’s temperature by checking the coolant’s temperature.

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Meet Victor Lukasso, the owner of V. Auto Basics. Through this blog, Victor Provides Insights on the latest tips, maintenance, repair, and techniques in the automotive world.