Check AC Radiator Engine Cooling

How to Check Your Car’s Cooling Fans Are Working.

If your car’s air conditioning isn’t blowing cold or you’re worried about engine overheating, a faulty cooling fan could be the culprit. I’ll show you how to check if both your engine cooling fan and your AC radiator fan are working properly. This guide is based on fixing the AC fan on my own VW Polo 9N.

Why Your Cooling Fans Are So Important

Your car has at least one, usually two, electric fans behind the radiator grille.

• The Main/Large Fan: This is the primary fan that cools the engine’s radiator. If this fails, your engine can overheat quickly, especially in traffic.
• The AC/Small Fan: This fan helps cool the air conditioning’s condenser. If it fails, your AC will be less effective. On many cars, like my VW Polo, this small fan can also help the main fan cool the engine if needed.

Crucial Safety Note: These fans can start spinning automatically, even with the engine off, if the engine is hot. Always keep your hands, tools, and clothing clear of the fan area.

How to Test If the Fans Are Working

The easiest test requires no tools and takes just a minute.

Step 1: Start Your Car
Turn on your car’s engine and let it idle. Make sure the engine is not already hot from a recent drive for this initial test.

Step 2: Turn On the Air Conditioning
Press the AC button to turn the air conditioning on. Set it to the coldest setting and the fan speed to low so you can hear the engine bay.

Step 3: Check the Fans
Get out of the car and look through the front grille. You should see and hear both cooling fans spinning. If it’s safe to do so, you can also open the hood for a better view.

• If both fans spin, they are working correctly.
• If only one fan spins, you have a problem with the other one.
• If neither fan spins, you could have a major electrical issue (like a blown fuse or relay), or both motors have failed.

What to Do If a Fan Isn’t Spinning

If a fan doesn’t start during the AC test, don’t assume the motor is dead right away. Here’s a simple trick to diagnose it.

The “Manual Start” Test (Be Very Careful):

1. With the engine and AC still running, take a long, non-conductive stick (like a wooden dowel or the handle of a screwdriver).
2. Very carefully, use the stick to gently nudge the outer edge of the non-spinning fan blade. Try to push it in a clockwise direction.
3. Watch your fingers! Only touch the very outer edge of the blade with the stick.

What This Test Tells You:

• If the fan starts spinning and keeps going: This is a clear sign the fan motor itself is faulty, usually due to worn-out internal carbon brushes. The electrical system (fuse, relay, wiring) is sending power, but the motor needs a little help to overcome the worn parts and start.
• If the fan still does nothing at all: The problem is likely not the motor, but a lack of power. You’ll need to check fuses, relays, and wiring.

How to Fix a Faulty Fan Motor

Once you’ve confirmed the motor is the problem, you have a few options.

Option 1: Try to Refurbish the Motor (For the DIY-Inclined)
You can remove the fan assembly and try to open the motor casing. Inside, you may find worn carbon brushes and a dirty rotor (the spinning part). Cleaning the rotor and replacing the brushes is a cheap fix if you can find the parts and are comfortable with detailed work.

Option 2: Replace the Fan Motor (The Most Reliable Fix)
For most people, the simplest and most lasting solution is to replace the entire fan motor unit. You can buy a new one, a refurbished unit, or a used part from a salvage car. This is what I ended up doing after my temporary fixes.

A Temporary Fix for a Worn-Out Fan

In my case, my small AC fan motor was worn out. As a temporary measure, I found I could get it to run for a single trip by manually starting it with a stick when I turned the AC on. It would run until I turned the car off. This is not a permanent solution, but it can help in a pinch if you need your AC and are waiting for a new part.

Final Thoughts

Checking your cooling fans is a simple but vital piece of car maintenance, especially before summer. A quick test with the AC can tell you a lot. If a fan has failed, the “manual start” trick helps you figure out if it’s an electrical issue or just a tired motor that needs replacing. Fixing it will keep your AC cold and, more importantly, protect your engine from a dangerous and expensive overheat.