Both radiator fans work when the AC is on but neither works when AC is off and overheats.


Asked by Nov 08, 2014 at 08:50 AM about the 2002 Chevrolet Impala LS

Question type: Maintenance & Repair

I know there are 3 relays for fan control. I switched 1 and 3 but didn't see any results.

11 Answers


Your fans work through a thermocouple relay. The sensor may be disconnected, lose, or corroded, or wire broke. One fan will come on when the vehicle temp hits between 180+ to 210+. Both fans come on when the A/C is turned on. You can rest assured the fans work. The thermocouple relay may be bad, of the temp sensor is bad. A good mech can by pass the sensors to see if the relay is good.

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Best Answer

Is that relay a fan relay? #1,2 or 3.....I'm thinking it might be the middle one, #2, do you know? I intend on replacing the temp sensor..... Thanks for your response......Al


Yes the relay will be the fan relay. It works as a thermocouple, or a switch controlled by temperature. When the heat gets hot enough the switch will move a heat sink or temp sensitive arm to make contact with the electrical circuit and the fan will come on. It is by all accounts a switch. In order for the engine to run at it's best efficiency and to reduce emissions, the engine must operate within a specified temp range. That is why the fan will turn off to heat up the coolant to keep the engine at a preset temp range. It is a constant read by the sensors to turn on and off the fans. The sensors have been known to be the weakest link, and are the easiest and lest costly to replace. Next is a reliable thermocouple switch in the fan electricity circuity which over time wears out and malfunction. This is more expensive as most people will insist on replacing the entire fan set-up because either they don't understand the system, don't have the knowledge to just change the switch, or are lazy and will make more money to change out the entire system.

1 of 1 people found this helpful.

I'm having the opposite problem. The fans work when the engine is hot but not when the Ac is on. In other words I have no AC until the engine warms up. Any idea what might cause that?

3 of 3 people found this helpful.

One of My fan works when the temp is 185-205 but the other one don't but if i turn on the ac is the same fan that comes on any ideas why the other one won't work at all ? Thanks

3 of 3 people found this helpful.

On a 2003 Chevy Impala if one fan making do it make the temperature gage Go up replayPlz

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Dual fans can be set up to have only one fan go on if the temp in the engine reaches a set level. Both fans will go on if a second level of temperature is passed. Also both fans will come on if the air conditioner is turned on. Other dual fans can have both fans come on at the same time, or like mine, both fans come on as soon as the ignition is turned on, engine running or not. Hope that answers your question. Is your car overheating and only one of two fans come on? If so, you may have a bad fan of . thermostat control.

Hello only one fan comes on on mine when car starts heating up before both of them worked

Is it OK to drive with one fan only working


Yes sir it is, IF, you don't have any issues overheating. When the A/C comes on, the second one should automatically come on. This helps cool the A/C and the engine works harder so it creates more heat energy. The second fan helps keep the engine within working range. If your fan stopped, check the fuses. Each fan should have a separate fuse. If using only one fan creates over heating, consider the cost of a new fan system, vs. an engine repair/rebuild/replacement. For now, if you're in the upper or middle part of the US, the weather is still cool enough to get by with half a cooling fan system. When it get hotter, be very careful. A couple of staying home and not eating out should be enough of a savings to get it up and running.


Guru8GMD, normal set up has only one fan come on to cool the coolant in the engine. The engine needs to warm up to run as designed. Normal conditions, including freeway or highway driving will only require one fan to operate. As I stated in the above answer, when the A/C is on, the engine uses more energy which relates to more heat. Also the A/C needs additional air flow to cool the freon. If the engine get over a set temperature, say 210, the second fan comes on to increase the airflow through the radiator and hopefully bring the coolant temperature back to desired levels. In my 69 Vette, I have both fans set to run constantly as soon as the ignition switch is on. The C-3 Vettes ran hot stock from the factory. The more horsepower you add, the hotter the engine will run. Think of it as a barn with 20 horses. they give off a set amount of heat. Add more horses, and the barn heat goes up. Make the horses work, and they get hot and the temp also rises. Living in Southern California, with slow traffic on the roadways and freeways, you can't always get enough speed to help cool the engine. Besides, I don't trust thermostats to always work. The newer ones will normally work with no issues for years, but with a $15,000 engine, I don.t want to take any chances.

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