Car Repair and Maintenance

Radiator Fan Not Working When AC On

Is your radiator fan not working when AC on? Guess what? It’s an easy fix, but you just have to be sure what went wrong, which this guide helps you with.

The sample scenario here is that when you turn on your AC, your cooling fan won’t turn on. That also means when you turn on your AC, the car seems to get hotter. At some point, it may reach 230 degrees Fahrenheit but you won’t see any warning light saying “overheating”.

Some parameters will cause your radiator fan to stop working even when the AC is turned on. And if the fan won’t blow at all (when AC is on/off), it could mean you need a fan replacement. Normally, your radiator fan should be working when you turn on the AC.

 Radiator fan not working when AC on

Radiator fan not working when AC on

Generally, factors including blown relay, blown fuse, bad temperature switch, low coolant, and frayed wiring harness, can stop the AC from working. That said, below are reasons/fixes for your radiator fan not working when AC is turned on:

1. Low or no coolant at all

Your radiator fan may not be working but you’d notice it’s not overheating (in many cases). The cause of this problem is that you have too little to no coolant at all in the reservoir. Note that temperature sensors are unable to read the hotness of the engine, but they tell engine temperature by calculating the coolant’s hotness.

On the other hand, the reservoir gets filled with air when the coolant level runs low, which results in the temperature sensor giving false readings.

How to fix

The solution is to check the level of coolant and the temperature sensor. Be sure you have sufficient reservoir coolant. The temperature sensor and coolant work hand in hand to properly read the temperature.

Nevertheless, even with the coolant on the proper level, the temperature sensor could still be faulty. Just don’t conclude that the temp sensor is faulty without looking at other signs of a bad temperature sensor, including:

Note, the signs above are as mentioned by AAMCO Transmissions Inc. Know when your temperature gauge reading is normal or not and have the temperature sensor replaced if it goes bad.

2. Blown fuse

A car fuse protects the electrical and electronic components in the event of a power surge, protecting the corresponding component’s electric bridge or surge damage.

When your car suddenly has a current surge that could potentially damage crucial electrical components, the metal strip on the corresponding fuse cuts, preventing the power from being transmitted to the major component. Thus, a blown fuse is the broken metal strip on the fuse.

How to fix

The solution is to get the replacement fuse installed on your car. Just visit your local hardware or home store with the blown fuse to get an exact replacement—NIH. It’ll also be helpful if you keep extra fuses so you have them whenever needed.

To install, follow your car owners manual and screw in the new fuse into the electrical panel socket.

3. Faulty fan controller module

In some vehicles, the fan control modules regulate the cooling fan and are found in the engine bay. The heat from the engine, dust, corrosion, etc., can cause this module to fail. Also, corrosion or dust can affect this element, typically depending on the location of the component in the car.

How to fix

Rhe fixing process involves locating and unplugging the connectors for the fan control module, removing the fan control module, and installing your new fan control module. You may require the services of a mechanic for a professional repair with the right tools.

4. Blown relay

The radiator fan receives power from the car’s electric flow, so many automakers install a relay to regulate it. It turns out the relays can get damaged, preventing current from going through to the corresponding vehicle components.

You should find the cooling fan relay fuse in the fuse box or a separate box next to the fuse box in your engine bay, depending on your car. Just refer to your owner’s manual to track the location of the relay and inspect it.

How to fix

You’d have to replace the faulty relay. First, turn off your engine, locate, and remove the faulty relay. You can unplug it by hand and then insert the new relay in the correct position. You need very little force to remove and install relays since the wiring and connectors could be brittle and delicate with age.

5. Faulty temperature coolant sensor

The powertrain control module is designed to oversee the general radiator fan operations. However, some automakers have different modules responsible for activating and deactivating the radiator fan.

Manufacturers use temperature sensors to detect coolant temperature and ensure communication with the PCM or the separate module. As such, if the temperature sensor fails, the engine control can’t tell if the coolant is running hot, which explains why the radiator won’t work when AC on.

How to fix

The solution is to have the temperature coolant sensor, which is advisable to contact your local mechanic for a fix with professional tools. This process can be a little complex, so it helps to let a mechanic do the work.

Read also: is your radiator aluminum? This antifreeze for you

6. Broken radiator fan

Your radiator fan could be broken if the radiator fan won’t work when AC is turned on. Cooling fans come with an electric motor providing the power for spinning.

If this motor fails, the fan blades lose the power helping them to spin. If only one fan is working, it could still be the motor that needs replacement on that specific fan. Sometimes, it could be a wiring problem within the line.

How to fix

The fix for your issue is to have your fan motor or the fan replaced. If the blade is the culprit, then that can be changed. But the common cause of faulty can is the electric motor.

You’d have to be sure the fan is faulty by slightly shaking the electric fan motor to see if it wiggles. If it’s not firm and steady, that could be the reason your radiator fan won’t work when you turn the AC on.

7. Wiring connection problem

You could have broken wiring connections if your cooling fan is not working but your AC runs and the engine is getting hot.

How to fix

Fluids such as oil can get dry, breaking the protective sheath on wires. Automotive wires also melt, getting damaged and exposing components. So, you need to properly diagnose the broken wire to fix and this can be done by a mechanic.

Bernard Juchli
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Bernard Juchli

Bernard Juchli is an experienced racer, mechanic and team owner who trusts Avon Tyres. Bernard is the lead driver and force behind his Big Dog Garage Race Team. He is the General Manager and Chief Mechanic of Jay Leno’s Garage. Bernard and his crew of seven are responsible for all repairs, restoration and fabrication of Jay’s incredible automobile and motorcycle collection.

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