Egine is cool no fan comes on... OK... Engine heats up, no fans come on. Not OK... Red light comes on and engine starts to over heat.... If I turn the Air Conditioner on both fans come on and you can drive the car like normal... I have replaced the thermostate last yr. so I first replaced the Temp sensor and no change. I just bought the Temp Switch but I haven't put it on yet.. Looking to see where it goes.. Any help why the fans work but wont come on with out the Air on?

More than likely the cooling fans or fan for the engine is not working, ether because of a fuse or the fan its self or the temp sensor that controls the relay for the fan. So first check fuse, then check the relay, then if those two are ok, then hook power and ground to cooling fan, if fan operates then ether the wire from fan to control temp sensor is open, or the coolant temp sensor if open, faulty, sense fan is not working this causing the a/c to be inop and the over heating of engine , but only at stop and go traffic do to the lost of air flow across a/c condenser and radiator.

Classic cooling fan relay failure.

Over heating the engine is a serious concern. With the hood raised you should hear the motorized fan turn on just behind the radiator as the engine requires additional cooling.. If you look in from the rear of the radiator you should see the fan blades.

This electric powered motor operates on a thermostat and when the engine temperature rises this fan should come on. I'm assuming from your description that when driving and air is flowing through the radiator as the car travels the engine is nor overheating.

Check fan motor thermostat, check fan motor and check wiring.

Wiring Diagrams related to the Honda Civic
http://www.wiringdiagrams21.com/category/automotive/honda-automotive/civic

Motor engine cooling fan only runs as engine temperature requires additional cooling.

Hi, Yes you have an air lock in your system, you may get this sorted by 1/. Removing one of the cooling hoses & try to blow with air.
2/. Drain all the system then put your heater on inside the vehicle & have the engine running & refill the system Start to do this from a cold engine. Please leave me feed back: Malcolm Campbell, Thanks.

A cheap cooling sensor might not start the fan. Make sure the one you or your mechanic bought is a quality product.

Welcome to Fixya

Sounds like you have a problem with the cooling system. First thing you need to check first if the auxillary fans are working from the time you are the engine is overheating. If the auxillary fans is not working then the problem would be the aux fan itself or relays. if Fan is working then you might have a poblem with the water pump.

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When the heat gauge shows hot and the hot light comes on the cooling fans must come on therefore there is a problem with the fans. The fuses been replaced so that is ok just check if it is not blown again indicating a short circuit in the fans. If that is OK check the wiring leading to the motor if it is not disconnected somewhere. Look on the engine where the fan heat sensor is by following the wires from the fan and check the connection. Change the fan heat sensor as last resort.

country driving at high speeds keep engine air cooled. but in city there is not much air to cool the engine. check the sensor for the fans. relay for fans must be ok, cause you said if you disconnect sensor then fans run. replace fan sensor. also make sure there is a proper amount of coolant in system. (do this first).

it will come on but only when the engine is very hot and the first fan cant cool it down that fast,, its turned on by a difrent heat censor so the engine needs to be realy hot to set the second fan running and it may even then only run for 30 seconds till the engine temp drops off,,, as long as the car is running in the normal heat range dont worry about it,,, if its cooking way up in the red,,,,,now worry about it,,fast too,,

Could be head,or head gasket blown.But change the thermostat and check to see if the cooling fan comes on after it warms up.Be sure not to have ac on.Watch the temp.be sure the fan starts and runs good,and then it goes off by itself.If the fan does not come on,then check for a blown cooling fan fuse,or a bad cooling fan relay.Be sure the cooling system is full,and has no air in the cooling system.Coolant sensor could be bad also(this is what tells the ecm to turn on the relay that controls the fan.When the radiator is full,and the engine is cool,or cold,start the engine with the radiator cap off,and look to see if coolant gushes out of the radiator while the car runs.If ti does,head,or head gasket is blown.