Does both fans need to run with a/c on if so what sensor controls the cooling fan its only comes on when engine heats up then cuts off when it cools the engine gets hot the a/c starts cutting off till it cools down 2000 honda civic .

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

Hi!!
Make sure the small hose going from the reservoir to the radiator and the orifice at the reservoir are not clogged. If OK, check electric cooling fan system, specifically the Coolant Temp. sensor, Fan Relays and Constant Control Relay Module (CCRM).
Electric cooling fan system consists of a fan and electric motor attached to the fan shroud.

• Engine temperature is monitored by the Engine Coolant Temperature (ECT) sensor.
• Fan is controlled by Constant Control Relay Module (CCRM) with inputs from Powertrain Control Module (PCM).

The electric cooling fan is wired to operate only when ignition switch is in ON position and engine temperature exceeds specified temperature, or when A/C is on and vehicle speed is less than 45 MPH. During hard acceleration, the Wide Open Throttle A/C Cut-Off (WAC) relay controls the A/C clutch and cooling fan. A signal is sent to PCM and then to the CCRM, where the module de-energizes the A/C clutch and cooling fan, decreasing engine load during acceleration.
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This should be normal operation of the fans they do not run all the time as most people think as the engine temperature increases the fans will come on to help cool down the engine once the temperature decreases then the fans will cut off and it will continue to cycle that way there is nothing wrong with that its normal. You will notice however that when you turn on the A/C the fan will turn on and stay on till you turn off the A/C this is also normal some vehicle have two fans one for the A/C the other for engine cooling unless your engine is getting too hot then they will both come on but normally one is for the engine cooling the other for the condenser A/C and this one will only come on when the A/C is running.

HOT WIRE COOLING FAN USING JUMPER WIRES TO BATTERY.IF FAN DONT RUN WHEN HOT WIRED FAN MOTOR BAD NEED REPLACING. IF FAN RUN WHEN HOT WIRED. CHECK COOLING FAN FUSE AND RELAY.IF ALL IS GOOD.YOUR ENGINE COOLANT TEMPERATURE SENSOR NOT WORKING.IT CONTROL COOLING FAN AT SET TEMPERATURE IF SENSOR OPEN OR FAULTY THE COOLING FAN WONT TURN ON.CHECK COOLING FAN WIRES FOR DAMAGE.IF ALL STILL CHECK OUT GOOD HAVE VECHICLE SCANNED FOR PCM FAULT.IF IT FAILS NO COOLING FAN WONT TURN ON.

Both the 2.2 and 2.4 liter engines use the computer to turn the fan control relay on and off. The computer gets it's temperature information from a coolant temp sensor that is dedicated just to telling the computer what the coolant temperature is. There isn't a seperate sensor or switch just for the cooling fans on either engine. It's very rare for the coolant temp sensor to fail and when they do there is almost always a corresponding performance problem as the computer no longer knows how cold or warm the engine is and will turn on the "check engine" warning lamp and set a corresponding service code. If the fans aren't working I would look first for a blown fan fuse [usually 30 amps or larger] or you could possibly have a bad fan motor. When working properly these cooling fans don't come on until the engine reaches about 218 degrees and then go off again as the temperature drops to about 210. The fan should come on anytime you have the a/c running while the vehicle is sitting & running as it needs the fan to run to remove heat from the a/c system. Once the vehicle is over about 35 mph the fan rarely comes on as enough air is being forced through the radiator and condensor to cool everything properly.

Cooling fans ( on radiator ) only come on when the engine reaches a certain (hot) temprature. There is a temp sensor threaded into the radiator end reservoir that switches a relay off and on that runs the fans. Either the temp sensor or the relay is probably bad. Normally , those fans will not be on if the car is moving , the air flow from just driving is sufficient to cool the rad. If you stopped and idled for a while , eventually the rad would heat up enough for the fans to come on.

It sounds like you do need a thermostat with your heat shut off and the gauge will raise a little then the car doesn't have that heat drawn from it indicating that you most likely do need a thermostat. As far as the fans coming on immediatly that could be a different problem it is most likely the coolant temperature sensor that tells the fan's when to come on. If this sensor says the coolant is hot the fans will come on immediatly. These are seperate problems as the coolant temperature sensor does not have anything to do with the cabin heating system. You should first check the level of your coolant is full, This could also cause your cabin heating system to perform poorly, and may have adverse effects to the engine cooling system. (fans)

if i disconect temp sensor fans come on cool engine but then no temp gauge

That's what I'd expect after unplugging.
This is sounding like a bad coolant temp sensor. Test it or replace it before you do anything else. Read this post on how to test an engine coolant temperature sensor

Test engine coolant temperature sensor Ricks Free Auto Repair Advice

The fan relay is not functioning correctly or the new sensor is defective.

Fifteen minutes! you have bigger problems than only the fans the fans are controlled by a thermo switch that is heated by the coolant, If you have no coolant the sensor cannot activate But fifteen minutes seems like you may have a headgasket problem and steam cannot heat the coolant sensor.OperationNotesThe electric cooling fan operates when the engine cooling temperature exceeds a certain value. The cooling fan on this engine is controlled by the Powertrain Control Module (PCM) . The PCM turns the cooling fan ON by grounding the coil of the cooling fan relays when certain conditions are met. When the A/C is requested, the cooling fan will also be turned ON.

Power for the cooling fan motors are supplied through Maxifuses(R). The cooling fan relays are energized when current flows from the fuses in the Underhood Accessory Wiring Junction Block, and through the relay coils to ground through the PCM. The Coolant Fan 1 Relay Control Circuit is grounded for low speed fans operation. During low speed fans operation, both fans run at a slow speed. The Coolant Fan 1 Relay Control Circuit is grounded for high speed operation. During high speed fans operation, both fans run at high speed.

IMPORTANT: When certain Diagnostic Trouble Codes (DTCs) are present, the PCM may command the cooling fans to run all the time. Perform the A Powertrain On Board Diagnostic (OBD) System Check prior to diagnosing the engine cooling fans.

For more information regarding the Charging System, refer to Charging System Description , and Charging System Circuit Description in Starting and Charging.

If a problem that involves the low speed cooling fan relay control circuit exists, DTC P0480 Cooling Fan Relay 1 Control Circuit should set. If the problem affects the high speed cooling fan relay control circuit, DTC P0481 Cooling Fan Relay 2 Control Circuit should set. A problem with the ECT sensor should set DTC P0117 Engine Coolant Temperature (ECT) Sensor Circuit Low Voltage, DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage, DTC P1114 Engine Coolant Temperature (ECT) Sensor Circuit Intermittent Low Voltage, DTC P1115 Engine Coolant Temperature (ECT) Sensor Circuit Intermittent High Voltage. Any of these DTCs will affect cooling fan operation and should be diagnosed before using the Electric Cooling Fan Diagnosis.

For more information regarding the Cooling System refer to Engine Cooling Fan Description - Electric, and Cooling System Description in Cooling System.


Here is the electrical schematic and how it all is suppose to work,
If you need any further help please contact me Thank you,Randy If you find this information helpful please give me a good rating

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