How to test radiator fan resistor

Bob Lincoln said:
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How do you test a bad cooling fan resistor?
How does a radiator fan resistor work?
How do you test a radiator fan with a multimeter?
What is the resistance of a radiator fan?

It's a thermistor (variable resistor) which has a negative temperature coefficient. So the resistance drops as temperature increases. There is no one value.

For reference, other cars generally run about 1000 ohms around 70F, and about 600 ohms near 190F or so. When cold, around 30F, they can measure around 13K ohms to 15K ohms. The resistance declines rapidly as it heats up.

If you are measuring open, first check your meter and leads - cross the leads and you should get zero or very near zero ohms. If you don't, your measuring device is faulty. If you do get zero ohms, make sure both leads are actually in contact with the thermistor leads. If you are reaching blindly into a connector housing, you may not be making contact with one or both pins.
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Thank you for responding. well, for the one installed on the aftermarket fan, it read OL, thank God I had the old fan i remove the thermistor and checked it woth outdoor temp around 75 degreess, it read 0. i put it on and now fan works again. Idk why the fan thermistor failed that was on there though.

Virtually all modern vehicles built today use electric cooling fans to help pull air through the radiator to keep the engine cool. Once the coolant temperature sensor detects that the engine temperature has exceeded acceptable levels, the cooling fans will be activated to keep the engine cool. Many vehicles come equipped with cooling fans that operate on more than one speed setting. This is made possible by routing their power through the cooling fan resistor. The cooling fan resistor is an important component, as it is one of the components that routes power for the cooling fans. For this reason, if you suspect that your cooling fan resistor may be having an issue, have the vehicle inspected by a professional technician, such as one from YourMechanic, to determine if your car needs a cooling fan resistor replacement.

this in an ongoing problem for me. my fans will not work without the a/c on. the resistor and wiring was replaced a few months ago. no change. fans still only work when a/c is on. is there an accurate way to test this resistor? thanks.

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whynotthinkwhynot

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#2 · Jul 27, 2011

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Can you monitor your engine temp using the electronic odometer test mode? The directions are detailed in the How-To archive in the dark blue banner just below the title of this thread. Engine temp will be displayed as [89 C], and will be displayed in Celsius.

Be eclectic.
---The Complete How-To Archive--

Moderating everything now, let me know if I can help. [poke]

the user formerly known as ZX3_Chick;4167595 said:
You're special aren't you.
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scodan

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Discussion Starter · #3 · Jul 27, 2011

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I have done that. I get a steady climb to 110 C and still no fans. I then turn on the a/c and it slowly cools down. I don't like getting my hoses this hot very often. Because of obvious reasons. I am wondering if there is a way to remove and test the resistor. thanks.

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deezx5

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#4 · Jul 27, 2011

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You can test a resistor that is part of electronic system using a multimeter, I'm sure it would apply in this situation too if you can find the specs. Honestly so many of these have been documented to fail that probably its easier to buy a new one. It takes 1 minute and no tools to remove the old resistor and put in a new one. If the wiring harness is burnt out that could be it too. In my case with my 02 I had to replace both parts.

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scodan

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Discussion Starter · #5 · Jul 27, 2011

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I have done that. Several times. I'm simply tired of spending money on parts if the old one is still good. Apparently there is no way to test these?

How do you test a bad cooling fan resistor?

What common symptoms indicate you may need to replace the Cooling Fan Resistor?.

Cooling fan never stops running even with the ignition off..

Cooling fan never kicks in and engine temperature increases abnormally..

How does a radiator fan resistor work?

Pre-Resistors (Radiator Fan Resistors) Power to the fan is routed through a pre-resistor, which allows the vehicle to control the speed of the fan depending on the temperature of the engine. An increase or decrease in resistance effects the voltage though the motor, resulting in the required changes to fan speed.

How do you test a radiator fan with a multimeter?

How to Test Radiator Fan with Multimeter.

Locate the fan on your car. ... .

Remove the fan motor connector..

Identify the terminals that supply current to the motor..

Set the multimeter to read volts by moving the rotary switch..

Connect the multimeter probes to the terminals on the connector..

Check the multimeter..

What is the resistance of a radiator fan?

When cold, around 30F, they can measure around 13K ohms to 15K ohms. The resistance declines rapidly as it heats up. If you are measuring open, first check your meter and leads - cross the leads and you should get zero or very near zero ohms.

test radiator fan resistor