Car radiator cooling fan testing with multimeter

Thread Starter

john2k

Joined Nov 14, 2019
219
My cars cooling fan has stopped working, I checked and changed the fuse and that seems to be fine. There are two relays powering the fan, it appears the fan is activated by two different relays. So chances of both relays failing at the same time I would think would be slim. Is there a way with a multimeter to test if a fan motor is faulty or not?

Another thing I guess I could try is to hook up a halogen 12v light bulb to the connector going to the fan and see if the bulb lights up.
 

Jon Chandler

Joined Jun 12, 2008
1,029
Some car fans depend on the ground connection being made by connection to the chassis by the mounting screws or by a jumper wire from the fan body and chassis. Checking for a solid ground connection is a good first step.
 

Thread Starter

john2k

Joined Nov 14, 2019
219
I disconnected the connector and used multimeter to read voltage across the pins on the connector when the fan is supposed to be on and I get a 14ish volt reading which indicates the connections all fine and the fan motor itself is knackered. I'm assuming electric fan motors are moving components so do eventually fail?
 

geekoftheweek

Joined Oct 6, 2013
1,201
While i'll agree it probably is the fan one good thing to do is back probe the connector with the fan still connected. You may have corrosion or damage that will show a proper voltage at the connector with no load, but as soon as you reconnect it won't be a good enough connection to power the load. Depending on the car fans can get expensive!
 

Thread Starter

john2k

Joined Nov 14, 2019
219
While i'll agree it probably is the fan one good thing to do is back probe the connector with the fan still connected. You may have corrosion or damage that will show a proper voltage at the connector with no load, but as soon as you reconnect it won't be a good enough connection to power the load. Depending on the car fans can get expensive!
I cleaned the connector on the fan motor itself and tried to power it with direct 12v from battery but it doesn't work. I got a second hand replacement from lower mileage car same age and that works when I give it direct 12v power.
 

Thread Starter

john2k

Joined Nov 14, 2019
219
Ok so I replaced the fan assembly with a second hand unit. Gave it a good clean before installing. Also tested it by plugging directly to the 12v battery and was working. One thing I noticed is that when I powered it via the 12v battery it just ran at a reasonable speed but not super fast. But after installing on the car and when the cars ECU turns the fan on when it needs maximum power, the fan goes super fast and loud. How is it the car is able to speed up the fan compared to when it's directly connected to the battery? It's only 2 pins. I would have thought plugging it directly to battery would have given maximum speed. Just a thought
 

MisterBill2

Joined Jan 23, 2018
18,167
It may also be that there is more to the control than ON/OFF. And it is likely that the connection from the controller was better than your test connection. As those fans may draw 20 amps or more there may be quite a voltage drop in a temporary hookup. And for an education, try connecting your voltmeter across the old fan and spinning it. Most of those PM fan motors are fairly good generators as well.
 

MisterBill2

Joined Jan 23, 2018
18,167
Once again, it seems that the system controlling the fan can run it at a slower speed. That is done for efficiency, because that highest speed uses a lot more power. So the slowest speed that provides adequate cooling is the best choice.
And ifyou like to learn you can take the failed fan motor apart and see how they are made. And it will have some really strong magnets as well. And you might be able to repair it and have another fan for when the used fan fails in a few years. Besides that, those fans make an interesting wind powered generator.
 

Reloadron

Joined Jan 15, 2015
7,501
Much of what you are asking really comes down to make and model of the car/truck. Not too many years ago when electric cooling fans came about for automotive applications things were pretty simple. Many of todays cars and trucks actually have fan control modules just for dedicated fan control. Next as was mentioned some automotive engine cooling fand draw high currents. A Google of "automotive cooling fan controller" will bring up all sorts of examples. If you only have a single or two wire fan things can be simple but if the fan uses a harness of several heavy gauge wires things get more complex.

Ron
 
Yes, we can test the car radiator fan with a multimeter. I write this article as very helpful how to test a radiator fan with a multimeter
Uh your article's English is so poor it's not helpful beyond click bait. "Voice of the digital multimeter with the electric radiator fan." ?? It talks lol.

OP, these car cooling fans are brushed DC motors. You can unplug the fan, and measure its resistance to see if there is continuity. A common problem is the brushes wearing out and the motor goes open-circuit, or the commutator wears out and it draws very high current and blows fuses or melts connectors/wiring.
Two relays can be a high/low speed system where two cooling fans are in series or parallel depending on the cooling demand the ECU commands.
 

Tonyr1084

Joined Sep 24, 2015
7,852
Mr fix it Welcome to AAC.

The last entry in this thread was back in July of 2022. Likely by now the issue has been solved. Nevertheless, you're welcome here to add anything you know or ask anything you need assistance with. Happy New Year.
 
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