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.

5 Answers

John Carson

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

John Carson

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.

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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?


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

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