Electric Fan Complex Design

Hi All, I am fairly new to the electronic's side of automotive so correct me where I am wrong. Regarding this post, my car is a Nissan Silvia S15. To reduce space in my engine bay and eliminate draw from the engine the clutch fan is being removed and being replaced with a twin electric fan setup from a Ford AU Falcon. I want to use the stock temperature sensor which provides a voltage depending on the temperature reading. I also want to have the fans switch to on when the AC is on, this is done using the ECU pin 9. These fans were made to run on LOW, supplying 6V to each fan in SERIES and on HIGH, supplying 12V to each fan in PARALLEL. Wiring Diagram for the AU Falcon is below In order to use the stock temperature sensor, I will be using a JayCar Voltage Switch for each setting (HIGH/LOW). Disregarding the ECU section of the problem the circuit diagrams I have designed below In Series on the LOW setting In Parallel on the HIGH Setting NOTE: the switches shown is the voltage switch which is not showing the input voltage to the switch and the temperature reading, this is just to make it easier to understand. To incorporate the ECU into the diagram, more relays were added to make sure that two voltages aren't inputted to the fan at the same time and that when HIGH setting is active, then the other settings are not. NOTE: The ECU acts as a ground switch, when the AC is on the ground is accessible. The 5 pin relays are only used as a guide as the program I was using didn't have the 4 pin relay Normally closed. Basically, my problem is that there are too many relays making this complex and that I have been told to integrate diodes to make sure that there is not backward voltage. Is there a simpler way to this circuit?

Revision ECU was connected wrong in the last picture

Google search "LS1 cooling fan wiring diagram"   http://www.motortopia.com/files/17204/album_wiringdiagrams/4c51a236c1209/CoolingFans04.jpg Connect G2, G10, and C11 at relays to ground not power as shown, since your control system supplies a positive control signal. F1 (E2 at relay) will be your positive low speed control. E10 (E10 and A10 at relays) will be your high speed control. A diode (1N5400 series) connected across F1 and E10 (band towards F1) will allow high speed operation to activate all relays. Also place a diodes in series with the low speed and high speed control outputs of your controller (bands towards the relays). These will provide isolation for the AC relay. A relay will be used to convert the ECM AC signal from negative to positive. Bosch type relay is fine (overkill actually). Connect terminal 30 and 86 to ignition power, terminal 85 to the ECM signal. Terminal 87 will connect to either F1 or E10 depending on how much airflow you'd lie through the radiator/condenser. Power the fan controller with a source that has power in run position, none in start. This will eliminate the need for a relay with much capacity as your diagram shows it powering both fans.

Regarding A/C fan control: Because you only mentioned one ECU connection for A/C operation (pin 9), that connection is probably an "A/C=ON" input that the ECU uses to increase idle speed when A/C is engaged. It is not a "control" output. The correct way to manage A/C condenser fan operation depends on the type of A/C system employed. If it is a Clutch Cycling Orifice Tube system, the fans should be ON when ever the A/C controls are in A/C, position, even if the clutch has cycled off. If it is a Thermostatic Expansion Valve system, then the fans can cycle with the clutch operation. I'm not familiar with your Nissan, so I can't help with specifics. But there are nuances to A/C integration into the electric fan system. I suggest you study and understand your Nissan's A/C control system well enough to get the interface correct. Cool project. That's a lot of relays! Good luck.

davep. wrote: Regarding A/C fan control: Because you only mentioned one ECU connection for A/C operation (pin 9), that connection is probably an "A/C=ON" input that the ECU uses to increase idle speed when A/C is engaged. It is not a "control" output.

Thanks for your query even though I don't really understand the two systems Regarding the image below from the ECU connection diagram for my car. Pin 9 acts as a ground for the relay to trigger LOW fan mode and Pin 10 for HIGH. So as far as I can tell this should work as it triggers a relay in the stock setup.

davep. wrote: Cool project. That's a lot of relays! Good luck.

Thanks!

Ween wrote: http://www.motortopia.com/files/17204/album_wiringdiagrams/4c51a236c1209/CoolingFans04.jpg

Thanks for your help Ween! The diagram is basically the same as that of the AU falcon and the first few diagrams I posted but with the diode setup it does eliminate one relay.

Ween wrote: Also place a diodes in series with the low speed and high speed control outputs of your controller (bands towards the relays). These will provide isolation for the AC relay.

I am confused as to where you mean to place this diode. I have constructed the diagram as described apart from this point and seems to be able to work well. One question with this design is that if both HIGH and LOW were on, would the relay (RLY2) be overloaded. Also if the A/C was on when either/both the HIGH and LOW were on would this overload the relay. The incomplete diagram for the described circuit

If my worries are accurate then I have devised a new diagram if not disregard this post. This is again getting to the point of too many relays. Sorry for overloading with pictures but it's the best way I can get my point across and for me to visualise it. Added RLY5 and RLY6

I am really confused. "To reduce space in my engine bay and eliminate draw from the engine the clutch fan is being removed and being replaced with a twin electric fan setup from a Ford AU Falcon. " Ok. Then you post a schematic (EC-14) "this is my car" that shows electric fan control. (The diagram with the red X over the fan control relays). The source of my confusion is probably that I don't understand how your car is currently configured. In the States a "clutch fan" is an engine-driven mechanical fan, with no electrics at all. If the diagram with the red X is your car's configuration, why not connect to the existing pin 9 & 10 fan control outputs? Use the 3-relay series/parallel LS1 scheme that Ween suggested. (The AU Ford schematic you posted is identical). The LS1 set up has been used in Camaro and Corvette for about 20 years. Works well, not complicated. The red X diagram shows the A/C clutch control. The ECM has an input from the control head, through the pressure switch pin-41 (it is a CCOT system) and an output pin-11 that controls the clutch relay. So again, IF that's your existing car, the A/C logic is already "in there" so pin 9 will respond to the A/C control. I apologize to Ween for butting-in. I didn't intend to, but I probably just confused things. Sorry. To the OP: Reassess your requirements. You ARE making this more complicated than it needs to be. I see redundant relays in your drawings. The 2 speed control can be done with 3. Plus one more to invert the (-) A/C control to (+) that your new controllers use.

nissans15 wrote: The incomplete diagram for the described circuit

This FINE as the complete set-up. I can't edit your drawing. You need to change some diodes around. Eliminate your "D1". (No connection between Lo and High) Put a diode in each controller output, band towards the relays. Put a diode in the output of Relay 1, band towards Hi control. Connect after the diode from the controller. ( Two diodes' bands joined together become Hi control. Either diode can "request" Hi speed.) Connect the controller's power to an ACCESSORY source. ACCY is OFF in START, so you won't need the start interrupt relay you have in your drawing. So this ends up being what I suggested in my post above. The 3-relay fan control, plus one relay to invert the A/C request. I don't see why you need more than this. Keep it simple. Make the changes in the diodes and re-post this with the changes. I'll review it to confirm you understand the suggestion.

Thanks for your help davep and bearing with me understanding this as I go. I now completely understand your confusion. I didn't realise there were two fans which I will be removing. (Due to not having the car with me at the moment - just planning phase) There is the viscous fan and a factory AC thermo fan which would be removed along with the clutch fun. Reference from a guy called omgpham "The factory AC thermo fan has the main function to cool down the AC condenser, but it follows certain conditions that are controlled by the ECU/ECM. When the ECU detects that the AC is turned on, it sends out a trigger to turn on the fan, BUT if vehicle speed is detected to be above 40km/h then the fan is disabled until the car slows down below 40km/h. This is a very important function because if the condenser isn't cool, the AC won't be cold and the condenser can reach high pressures and EXPLODE!!!" I will work on the circuit diagram tomorrow evening when I have a bit of spare time.

Also if D1 is removed how will power get to fan 1 on high mode?