ale5six1

ok so I have a DX CRX with a b16 swap and obd 0 to 1 conversion harness with the MPFI to DPFI adapter also. I'm running a p28 ecu that has Hondata s300 installed and I want to be able to control the fan temp for turn on. but the A12 wire from the Wire harness is not connected at all to anything. its just cut at the Wire Harness that runs upto the passenger side headlight next to the radiator fan relay.





from what I understand one of the wires going to the fan relay should be the wire that runs to the a12 on ECU which is for FanControl.

as of now the wiring going into the relay is from what I can tell...

A= Positive wire directly to fan
B= runs to main wire harness connected to a black wire with a yellow strip running down the side
C=runs to black wire with silver rings around it every few inches. (I think this is a ground wire??)
D= goes to the ground on the fan switch that is mounted on the thermostat housing. (now the positive from this same switch is running straight to a 12 volt output with a 15 amp fuse in the wire, is this correct?)

any help is greatly appreciated, as I have been struggling with this for weeks now.

BTW, the ground from the fan runs straight to the body of the car, not sure if thats correct either.

jdm_rb20

This may help. It's directly from a 1991 CRX FSM, but use at your own risk. On the linked page, you will be able to read my personal notes about how the systems operate the fans. You will probably need to read those notes to understand how the factory setup changes voltage on 1 of the ECU pin's, and that signals the ECU to change the voltage on the ECU pin output (yellow wire).

Anyway, hope this helps..use at your own risk and study your wiring too.

https://honda-tech.com/forums/honda-crx-ef-civic-1988-1991-3/1991-civic-hatch-need-air-conditioner-expert-3140116/
https://honda-tech.com/attachment.ph...1&d=1366514538

jdm_rb20

...

jdm_rb20

Where you see the 2 exclamation marks (1red & 1blue, at 2 different ECU pins)....that is where you will find battery voltage when the system is "at rest" UNLESS otherwise changed by a) the AC system turning on, or b) the ECU changes the yellow wire to a ground signal that, then, triggers the relay for the condenser fan relay.

ale5six1

Added: I have a half sized aluminum radiator and only 1 slim fan.

holy hell that looks waaaaay more complicated then I thought it was! LOL BTW I have no A/C or power steering so hopefully that takes some of those things in the diagram out of the equation.

I thought the only thing that consisted of the wiring setup for fan was, ECU, Coolant sensor/radiator fan switch (located on thermostat housing), the wiring that goes to the coolant sensor on the block below the vtec solenoid that the ECU uses to read temp. the relay and of course the fan itself. also there is a coolant temp sensor that is used for the temp readout in the gauge cluster, but thats not really required for fan to work...

am I thought far off? or have I simplified it too much?

ale5six1

BTW Thank you very much for the diagram! I'm starting to understand it more, I think my main concern is the center part correct? all the rest seems to be for A/C use, what about the pressure switch?? I havent seen that or heard it mentioned before in other searches.... for A/C?

jdm_rb20

This is pretty close to the basic cooling system (minus all the AC stuff).

jdm_rb20

Your cooling fan setup is ONLY the lines and components directly under the "IG2-a" and proceeding south to the 2 Grounds under the fan relay.

jdm_rb20

Yes the "pressure switch" is for the AC. consider it a "manual switch". It has no real voltage...it's just ON or OFF, depending on physical conditions. If there is sufficient freon pressure, the switch is ON, and it lets the AC stuff turn on (including both fans because it provides an alternate ground to the Radiator fan relay).

The radiator fan gets its signals from the radiator fan relay. The radiator fan relay is given permission to operate the radiator fan by ....(drumroll please??).....the coolant temperature switch. The CTS is also like a "manual switch." If the physical conditions (sufficient engine heat) are correct, the CTS will allow current through it. Now that the current is moving because it has a path to GROUND-, the relay turns on the fan.

That's the ultimate rule: Current will only power something if there is a path to GROUND- on the other side of it. In this case, I don't know that you even need the wire to the ECU. On the other page (and a little on this page in one of my previous posts), I noticed a relationship between the AC system providing the alternate GROUND- to that wire, and the ECU (coincidentally??) changes the other AC wire (yellow) to a GROUND- signal for the AC compressor relay to work. I am a little fuzzy on the entire significance of that ECU wire that monitors the fans' (both of them) shared GROUND- signal.

jdm_rb20

If you are engineering your own system, your basic design would have 4 wires to the relay:

1) FUSED 12v power source (constant or ignition switched...up to you)
2) Ground- signal wire from the CTS.
3) Ground- wire from the radiator fan to the relay
4) Ground- wire from the relay (carrying the ground- from the fan) to the actual BODY/CHASSIS ground-.

To wire the CTS:
1) One wire is already wired to the relay per the instructions above (step #2)
2) The other wire is connected to BODY/CHASSIS GROUND-.
***additional note: CTS sensors don't always have 2 wires....sometimes they are AUTOMATICALLY grounded just by being there...thus eliminating the need for a wire from CTS to BODY/CHASSIS.***

Finally, the radiator fan:
***The fan relay and CTS work together to provide the GROUND signal to the fan's GROUND wire, so that wire is already connected.***
1) The fan's 12volt "hot wire" is spliced onto the "FUSED 12v power source" for the relay. The OEM fan setup also has a "FUSED 12v power source" splicing to power the relay and the fan simulateously.

zrickety

iTrader: (1)

The stock fan setup should be all you need. It's a temp switch, relay and the fan. Here is a diagram that may be a little easier to read.

ale5six1

ok does it matter which power and ground wires goto where on the relay? because it has the 4 connections A,B,C and D. as of now..
A = power to fan
B= to wire harness which I'm not sure is connected properly
C= constant ground
D= Ground on radiator fan switch located at thermostat housing.

so from what your saying I need to switch the power wire from fan to be connected to constant 12v and run the ground wire from fan into the A position on relay?

jdm_rb20

I don't feel comfortable trying to "supervise" when I am not there in person. Please study the schematic of the radiator fan relay in the original schematic setup. It should be similar. If you have any of the OEM wiring still in place, the colors may the same as what is listed. If not, study the relay you are using to determine which wire is supposed to have which input/output.

I will not that for the 12v FUSED power source (which is spliced to the fan AND the fan relay), you will have to choose the source. If you choose an ignition-switch controlled source, then your fan will turn off when the key turns off. If you want the fan to continue cooling the radiator until it is sufficiently cooled, then you want to use "constant" 12v power source.

ale5six1

ok so I'm going to rewire the power as per diagram and instead of using the CTS ground to control the relay I'm going to use the ground from the A12 on the ECU. (reason why i want to do this is b/c I want to be able to control when the fan turns on by using the Hondata Protection section) now do you think this will overload and fry the ECU?

jdm_rb20

I make no guarantees about things I don't know about. I'd research it a bit more before I did it. However, I can theoretically ask: How does the ECU know what the engine temp is? Theoretically, I can asssssssume that even the Hondata ECU still needs input from a temp sensor. And then (theoretically), the Hondata ECU will honor your wishes and send signal to the fan relay at the temperature that YOU specified.

After all, the Hondata ECU lets you pick the temperature when the fan comes on.....but the ECU needs to know the temperature from a temp sensor.

But actually, it may get the temp from another sensor. I always THOUGHT (key word: thought) the CTS is a simple ON or OFF switch. I think the ECU probably gets the actual temp from a variable-resister type of temp sensor located somewhere else on the engine???

I would keep it simple and just use the CTS and relay just as the OEM setup operated. After more research, you may be able to tweak the wires later to make it work with hondata.

jdm_rb20

Please note that zrickety has posted a diagram from a different vehicle than I posted. At this point it doesn't matter which way you choose to wire the relay. In the car that I posted, the relay is wired to open a path from the fan to the GROUND-. In the car diagram zrickety posted, the relay allows a path from 12v+ to reach the fan's 12v+ wire.

Both ways work equally. The CTS controls the relay. The relay generally opens a path between 12v+ and GROUND-. The fan is on that path and gets to operate because it is enjoying the flow of current on the path. Potato = Potatoe.

ale5six1

alright update!
so the wiring setup is very weird but its working, there is constant power to the B input, constant ground to the C input and D goes to positive power once the CTS switches on. because the CTS has constant power from battery and once temp reaches 195 degrees the switch clickes on and allows power to run to the D input on the relay.
Questions...
1. so once the switch it activated there are 2 inputs getting 12v and 2 grounds... so that sound normal? I thought relay was suppose to have 3 ground and only 1 power?

2. pardon my ignorance i have no electrical experience, but when i was testing the relay once 12v and ground is applied to the C&D side of the relay then it links the A & B sides of relay correct? (i tested this and it had continuity between A&B once power and ground applied to C&D) so if one side of the A&B on relay has power, then once the C&D are powered with ground and positive that will make A&B linked together allowing both sides of A&B to have 12V power?

3. so it seems all the CTS switch does is allow power to pass through it once the coolant reaches a certain temperature correct? because once the temp reached 195 degrees the relay clicked on, as it was now getting 12v into the D input on the relay coming from the CTS.

ale5six1

yes the B16 motor has a temp sensor located below the vtec solenoid near the distributor on the block, which is a Green plug that plugs into a sensor with a green plastic input on it. which tells the ECU exactly what temp the coolant is.

so based on that... could I skip using the temperature switch and just run constant power to the D input on relay and then take the now constant ground running from the C input on the relay and connect it to the ECU Fan Control ground?
I was told that it can overload the ECU if you have too much power running the ground on the ECU, would I be able to prevent an overload by inline fusing the ground with a 15 amp fuse?