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Old 08-01-2001, 05:11 PM   #1
BoM
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Default When does the cooling fan come on?

okay, recently i have been having overheating problems on my gsr....soo im just gonna change a few things....coolant 50/50 mix, head gasket, higher psi radiator cap ect...but now i opened my hood when its hot as heck...but the fan isn't on...

i think this is the culpurate u guys think? when does the fan come on? how can i find out if it is this?
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Old 08-01-2001, 05:37 PM   #2
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Default Re: When does the cooling fan come on? (bommiE)

simply, your cooling fan should come on when the temp gauge reads just below the halfway mark.. or when the coolant temperature reaches approx. 180-200 degrees ( i think its easiest to read the gauge Click the image to open in full size. )...
An easy test to see if the Thermal switch is actually working would be to "jump" the terminals in the thermal switch connector with the ignition switch in the "on" position.. under normal conditions the cooling fan would come on when the terminals are jumped..
The cooling fan should be receiving power at all times and the ground is on the switch/timer circuit..
Could have a bad "cooling fan relay", easy test.. just swap the relay w/ the A/C Condensor Fan or A/C compressor relay ( assuming you have a/c) located in the same fuse block underneath the hood..
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Old 08-02-2001, 11:13 AM   #3
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Default Re: When does the cooling fan come on? (BreakStuff)

I am having the same problem in my 89 Civic Si. I checked the wires coming out from the back of the block (the two nipples) and they are connected, but the fan doesn't come on. We switched the wires around and it still didn't work.

Where is the thermal switch located? Also, where are the relays? I want to check them all out.

Thanks!
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Old 08-02-2001, 01:58 PM   #4
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Default Re: When does the cooling fan come on? (bommiE)

Does the TW switch feed to the ECU ? and then the ECU sent the neg. signal to
the tan relay ? Where is that two diode device located that i see in the manual ?
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Old 08-02-2001, 06:15 PM   #5
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Default Re: When does the cooling fan come on? (BK101)

First off, lets not confuse a "thermal switch" w/ a TW Sensor, they are very similiar but have different jobs to keep the car running efficiently.. Thermal switch controls the cooling fan only and the TW ( coolant temp sensor) tells the ecu the temperature of the motor and cooling system...

In your case Breaka, you will be looking for a sensor located on the thermostat housing, this will be your "thermal switch" which has 2 wires, colors should be black and yellow w/ a green stripe, take the connector off the sensor, connect those 2 wires together ( ignition on ) and the cooling fan should come on..

As for you BK, yes you are on the right track..but in most cases the only cars that are wired up that way are the ones w/ a timer function that will tell the fan to run although the car is not running, the rarely get that info from the ecu and have their own timer unit located elsewhere in the car, the diodes you are looking at are part of the a/c unit and tells the cooling fan along with the condensor fan to both turn on when the a/c is turned on..

ok, so we now know that the cooling fan has power applied to it at all times, every now and then I have customers that tell me their "cooling fans never shut off" reason being.. the ground wire is usually shorted somewhere in the system, most likely, the metal fan shroud.. this ends up kiling their battery and yadda,yadda,yadda..

Thermal switch is what tells the fan to come on, one wire of the switch is grounded and the other side is what sends that negative/ground signal to the relay, turning on the cooling fan... this is the same w/ most import cooling fan systems.. some domestics are just the opposite.. its just gets a little more confusing when they involve the ecu and timer circuits...

As for the relays, they are located in the fuse block undeneath the hood and should be labeled on the cover...




[Modified by BreakStuff, 2:24 AM 8/3/2001]
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Old 08-03-2001, 06:01 AM   #6
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Default Re: When does the cooling fan come on? (BreakStuff)

Breakstuff, thanks for the breakdown..

Ok, I think I got it. My fan comes on as so as the car ignition is turned to second position.
The weird thing is that when my battery dies, and i get a boost
the fan does not come on with the boost, it turns on after the temp gauge gets half way. So the fan switch is reading and working. But from then on, the fan stays on as before. So i don't think it is a short. please give me your input.
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Old 08-03-2001, 08:04 AM   #7
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Default Re: When does the cooling fan come on? (BreakStuff)

Thanks for the help BreakStuff. I will take a look around tomorrow and try to jumper that connector to see what the deal is with my cooling fan.
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Old 08-03-2001, 07:42 PM   #8
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Default Re: When does the cooling fan come on? (breaka_1_9)

Hey Guys, first off..Your welcome! and happy to help : )

As for your problem BK, thats a good one.. what year and model car are we talking about here? I would have to take a quick peek at some schematics to see what is involved w/ your cooling setup..
Sounds like your Thermal switch may be sticking, but the more I repeat that to myself, the stupider it sounds Click the image to open in full size. I have yet to see a TS stick, Its a thermal probe and either it works or it doesn't!

Got a Digital/Volt /Ohm meter? you could check for continuity between the sensor terminals when the sensor reaches approx 180 degress, you should have continuity..
when the motor cools the continuity shouldn't exsist..

Might be easier to take the sensor out of the vehicle and do this test in the kitchen using some boiling water and the refrigerator ( no joke, we test like this all day long.. got a stiff oil pan gasket? just stick it in the microwave for a few seconds! Click the image to open in full size.)
The proper way would be reading the resistance values, but I don't know them off the top of my head... GL
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Old 08-06-2001, 08:51 AM   #9
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Default Re: When does the cooling fan come on? (BreakStuff)

Man, Breakstuff thanks a million.
I car is a 1991 GS auto.
But I don't think it is the thermo sw. because when i unplug the connector from the
thermo sw. the fan is still running. It's crazy a small circuit like this.
But please check for me if u can.
Thanks
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Old 07-06-2009, 05:57 PM   #10
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Default Re: When does the cooling fan come on?

Hey guys,

ok, here's my mystery...start the engine and allow it to reach normal operating temp(just below half scale reading on temp gauge). Cooling and condenser fan's kick in- all is as it should be, I think? Not certain about the condenser fan coming on simultaneously? The weird part is... the fan's stay on continuously until I turn on the heater, then approx. 1 minute or so later they shut off.

The engine never overheats and the thermostat is brand new and operating properly as far as I know(Coolant starts flowing as it should upon reaching operating temp on gauge). This engine has new timing belt/tensioner and water pump, new thermostat, new thermoswitch, new coolant etc. Runs pretty good.

Does anyone here know how the thermo "sensor" contributes to this system?Mine-I believe-is located directly below my distributor. As mentioned above, I've replaced the thermo "switch" on the back of the engine block.I also swapped the cooling fan and condenser fan relays as they are identical. There was no change in operation.

Is this normal for this year civic(1990 1.6l Si hatch)?A friend of mine has a 1.5 l and his cooling fan kicks in and out sitting in the driveway after reving the engine up at 2500 rpm and then letting it sit at idle.

Thanks for any and all help!

Also, my tach barely comes off zero when I hit the throttle. It moves ever so slightly. Is it possible the ignition module in the distributor is causing this?

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