Cooling fan on/off

[California98Civic]

Originally Posted by oldtamiyaphile

A hypermiler's radiator fan should never run.

Only time mine run is in the middle of summer with a full grill block - even then only really if towing. In normal driving the thermostats rarely even open fully.

Ecky has your answer. I also live in a part of Cali where "mountains" of 500 feet are common. And there are a couple 800-1100 footers in my monthly round. My grill is heavily blocked. I find on the freeway in the summer I sometimes need to run the heater to keep engine temps below my 206* alarm on my Ultra Gauge. The on/off cycles of my pulse and glide seem to affect cooling by the ECU Not sure why.

Turning the rad fan on, on demand would be awesome.

[California98Civic]

Last night I investigated further where how to wire fan in a way that is stealthy and easily reversed for smog. I think the ECU itself might be the "temp switch" reading the coolant T and deciding when to send power to the fan (maybe). Right now, I am considering using the wires I connected directly to the battery for my onboard charger. They must be live all the time. Smog has never protested them, and I would avoid cutting into OEM harness. Only cut I want to make is to the radiators connector side,if possible.

[Occasionally6]

Most likely the ECU earths the switching side of the cooling fan relay. The way to check is to find the wire from the relay into the ECU and measure the voltage present with respect to a ground - all wires still connected.

You should see battery/alternator voltage until the fan is switched on by the ECU. With the fan on, the wire will be earthed through the ECU and so have zero voltage with respect to ground.

To switch the fan on manually, connect the wire between the ECU and fan relay to ground via your switch. Leave the wire connected to the ECU - use a splice. That will allow the fan to be switched on in parallel with the ECU switching i.e. either the ECU or your switch will activate the fan.

The current drawn by the relay is small, so virtually any switch can be used.

[California98Civic]

So I bought a switch today and was testing it from different points, then suddenly I realized, my car had a n AC system that I took out, but it still has the harness. Here is the FSM diagram. Why don't I just use the AC harness for access to power for the radiator fan!?



Basically, the underhood consenser fan relay controlled the condenser fan. I could maybe get power there, and use the AC switch as my fan switch? Hmmm... That does not seem correct.

[California98Civic]

Here is a picture of the compressor fan motor you can see on the left of the above circuit diagram:



That connector test connected to rad fan motor connector ( follow the red wire from the upper right at the radiator to the lower left):



Here is the switch temporarily wired up through the firewall:



It works! But as I expected, the compressor fan connector only gets power when the air conditioner is turned on. That is not a very desirable set up. But it works, and it will be easily reversed when finished.

[California98Civic]

Finished and posted result and pics on my modding thread:
http://ecomodder.com/forum/showthrea...tml#post565432

[ASV]

my dad told me a story about a truck he had
the radiator was bad and he didn't have the money to replace it
so he put a 55 gallon drum in the back and ran a rubber garden hose to it

no fan no radiator just a big old thermal battery and a thermostat
according to him it worked perfectly until he had the money to replace it

[California98Civic]

Well, I don't have a 55 gallon drum, except for water recapture. But also, I became dissatisfied with this set-up for the radiator fan switch. I HATE switching on the AC and the cabin fan in order to get power to the radiator fan. What a waste. So I am experimenting with other power sources under the hood. I also think I might relocate the switch to near the shifter so I can access it more easily for DFCO (alternator on) cooling glides.

The basic idea of the radiator fan override is working great though. I can control the coolant temp spikes and keep them under 200, so far, almost all the time.

[jeff5may]

Ok, so per the wiring schematic you posted, you should be able to control the fan at will while the ignition is on. Use the Blu/wht wire at the underhood junction box or at the a/c thermostat. Splice into the wire and run a control wire to your switch. Ground the other switch terminal. The end. Low power control of what have you.

Send it to the shop