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Air Conditioning and Coolant
Honda Accord
Heating Ventilating and Air Conditioning

Why would the AC fans not come on when you turn on the AC?

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2015-07-17 17:40:21
2015-07-17 17:40:21

I have a 1994 caprice 5.7 liter v8 with two cooling fans. The second one is only supposed to come on when the a/c is running. It does not due to the Engine Control Module (computer brain) not telling it to. The fan was tested with a direct wire and it works fine. The options are to replace the ECM or run a jump wire where the relay for you fan(s) are and connect a toggle switch to it and cut it off and on as needed. .

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You probably have a bad temperature sensor. TS reads the temp of the coolant and turns the fans on when hot enough. Without it the fans arent controlled by temp. When you turn on the AC the fans always come on.

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When I turn my AC on sometimes they come on and sometimes dont, causing it to overheat. I checked the fans by hotwiring from the battery and they turned on everytime.

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The cooling fans are set to come on when the coolant reaches 224 degrees (low speed) and 240 degrees (high speed). If they do not turn on (without the AC) then either your coolant does not reach 224, or the switch that turns them on and off is bad. The switch should not be hard to replace, or too expensive. Since you mention that they do come on with the AC, then we know it's not the fans themselves.

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A fans blades are driven by motors. Since there are both AC and DC motors, fans can be AC or DC. The fans in your computer are DC fans. Your ceiling fans are AC fans. (Thanks for fixing my answer)

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check to see if your rad. fans come on when you turn on your a/c the compressor will not work if the do not come on

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Yes, when the a/c is used the engine works harder which rises the temp of the engine then turn the fans on to cool the radiator.

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I believe that the fan(s) come on automatically with the AC system. Someone else might be able to confirm that. If so, then I would guess that you need to find and replace the temp sensor/switch for the fans.

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check the relay / check the temp sensor / try turning the fan on by turning on the AC - fan should come on when the AC compresor turns on /

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they do for the ac they only come on when the engine temp is peaked about 210 deg

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Electric fans on vehicles only run when necessary,,,over heating or the temperature getting near a dangerous level. They just do not come one when the vehicle runs. Normally they WILL come on if you turn the AC on because of the added stress on the engine.

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The 2nd fan on this car is for extra cooling when the AC is turned on, if you turn on the AC both fans should run; the relay is the first place to look if that fan is not coming on.

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The fan engagement threshold is set high in those cars. I have a 96 myself and it gets above 220 before the fans kick in. I would by a programmer for the car such as hypertech to set the fan engagement to a lower level. Or a cheaper solution would be to hook up a toggle switch for the fans to come on when you need them. This is all assuming your fans work at all. Next time it heats up, turn on your AC. If the temp falls, your fans are in working order :).

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It is normal for a little vibration with the air conditioning on due to the compressor working , fans on , and engine running a little warmer. On at least 92-96 Toyota's the fans automatically come on when the ac is turned on

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The cooling fans will run when there is a signal calling for them to come on. High temps will do that. Also anytime the ac is on, a fan will run. Try turning the ac off and see if one of the fans stop. Do this when the engine is cold. If the fans run anyway, check your fan relays, they may be stuck on.

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does the ac just stop or does the defrost also come on out of the blue?

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The AC takes the moisture out of the cabin air and that helps clear the inside of the windshield from moisture faster.

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Turn the defroster on. If you have a separate AC switch, turn it on also. The AC should come on with the defroster automatically, but might not. If no AC, set the vent control to outside air instead of recirculate.

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If you have the AC turned on the fan will come on to help cool the engine from the load on the engine. If your car has dual fans only one should come on at that time and the other one would come on when the sensor obtains the required heat range.

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Very possible your temperature sending switch is bad. If both fans work with AC, then it's also possible you have a wiring issue.

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answer my own question the fans come on at a set temp on the 99 aurora it is 229 degree and kick off at 219 had it check out

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Whenever the AC is turned on, both cooling fans also come on. Otherwise, during normal operation only one fan comes on when activated to maintain correct engine temp.

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as soon as the ac is turn on the cooling fan should come on if not there is a problem with that take it to a ac shop thay can find it fast ..

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At least one of the fans should come on. If it does not, then look for blown fuse, defective compressor fan relay, loose of broken wiring, or a bad fan motor.

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Most common problem LOW FREON


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