Sorry for dredging up an old subject, but I wanted to provide some explanations for those things that seem to have frustrated a lot of people when attempting to install the DUAL FAN CONTROL MOD:
First and foremost, remember that you are using two separate fan control switches to accomplish your goal (which is to control each of your two cooling fans independently from each other WITHOUT disabling your factory fan setup). In order to do that you need two fan switch kits: the HAYDEN 3652 (that comes with a fixed temp thermal switch and a separate heavy duty relay) and the HAYDEN 3647 (which has an adjustable temperature range). Second, remember that the electrical control system in these cars is based on the ‘SWITCHED GROUND’ theory, which means that all switches and controls receive a constant supply of positive power, but with an interrupted ground circuit that actually provides the system control. This is assumed to be more reliable since there is less voltage fluctuation in the ground circuit than in the positive power circuit, thereby creating a more stable feedback signal from the control system of the vehicle. I don’t know if this is true or not. But, none-the-less, the ground control circuits are what we’re interested in for this modification.
Now, the 3652 switch is a normally open thermal switch that closes when it reaches it’s predefined trigger temperature. In this case, we’re going to use it in conjunction with a simple ON/OFF toggle switch to be able to go back and forth between the factory system and our modified system for controlling the primary cooling fan operation. The 3652 turns the fan on at a lower temperature and the toggle switch simply allows us to switch between the factory setup (toggle switch in OFF position) and the modified setup (toggle in ON position). This is accomplished by running a ground lead to one terminal on the thermal switch, then a lead from the other terminal to the toggle switch, then a lead from the toggle switch to the ground lead (GREEN/WHT wire) on the factory primary cooling fan relay. When in the ON position, the HAYDEN thermal switch is engaged and will turn on the primary cooling fan at a lower temperature than the regular factory ON setting. When in the OFF position, the system operates as the factory intended. NOTE: the heavy duty relay that came with the 3652 switch is not used in this circuit. As luck would have it, we’ll need it for the secondary fan control circuit.
The 3647 switch is a little more complex as it allows you to set your own “ON” temperature via an extremely small potentiometer that is set using an extremely small flat head screwdriver. This switch was designed by HAYDEN to run up to two cooling fan motors directly, which in our case would require disabling the factory setup. Since we don’t want to do that, we need an extra component to allow us to integrate the 3647 switch into the secondary cooling fan circuit WITHOUT disabling the factory setup. That is where the HD relay from the 3652 kit comes in! The reason we need a separate relay for this circuit is because the 3647 is a POSITIVE lead thermal switch (provides (+) power to the fan motors directly from the thermal switch). Because we’re going to maintain the factory setup (switched ground), we need a second relay (controlled by the HAYDEN 3647 thermal switch) to handle the switching of the GROUND signal for the factory secondary fan relay. In other words, the first relay supplies power to the coil of the second relay, which in turn completes the ground circuit to the factory secondary fan relay thus turning on the secondary cooling fan. Pretty straight forward!
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"Wire the Hayden unit as per instructions with one difference: Connect the Fan (+) wire to #86 on the SPDT relay." Is this wire, the wire actually go to the existing secondary fan motor? The 8647 relay has two wires, blue and orange, which the diagram says should go to the fans. Am I leaving blue and orange unconnected?
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Yes and No. Connect the orange wire to the #86 terminal (+) on the HD relay. Terminal #85 (the negative side of the coil) goes to ground (-). This is so that when the HAYDEN thermal switch reaches it’s “ON” temperature, it will send a positive signal to the HD relay coil instead of directly controlling the fan motor as HAYDEN had designed it to. The HD relay is what actually turns on the secondary cooling fan by completing the ground circuit that you’ve TEE’d into on the secondary cooling fan relay wire (the GRAY wire). It goes as follows: When the 3647 reaches it’s “ON” temperature, it sends positive battery power through the orange (and blue) wire, which toggles the HD relay, which in turn completes the ground circuit to the secondary cooling fan relay, which in turn turns-on the secondary cooling fan. NOTE: Tie off the blue wire with electrical tape, it is not needed in this circuit (make sure it is well insulated since it will be live whenever the system is in operation).
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Also the 3652 relay and the Hayden 8647 have a red "Power Supply" wires that in the diagrams go direct to the (+) on the battery. Is this correct?
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Yes, these wires go to the battery, or a convenient power lead that is always HOT.
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Also they both have a yellow wire that the diagram says to connect to a 12-volt connection that is controlled by the ignition. What happens here?
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For the 3852 (primary fan circuit), you’ll not be using the HD relay, so set that aside for now. For the 3847, the yellow wire on that relay is what controls the power to the relay coil inside the thermal switch. If you wire it to an IGNITION ON power source, as soon as you turn your ignition on, the HAYDEN system is also turned on. Ignition off, HAYDEN off. This is to prevent the fan from running after you turn the car off. However, some people prefer to allow the secondary cooling fan to run even after the ignition is turned off. This allows the secondary cooling fan to continue pulling air through the radiator until the coolant temperature drops below the “ON” temperature level. Once the coolant reaches that level, the thermal switch then turns the fan off automatically. (If you want the system to function this way, you will need to tie the yellow wire into an ‘always HOT’ battery lead). It’s really personal preference.
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Does anyone have a diagram of how the Hayden 3647 is hooked up, telling me what goes where?
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I know that this thread is over a year old, but I’ve attached the wiring diagram I created to aid me in the construction of my system. Additionally, instead of simple ON/OFF toggle switches, I used ON/OFF/ON switches (STDP) that have a ‘center off’ position (I used this type of switch on both circuits). That way I could either:
1) run the factory setup (center ‘off’ position)
2) run the HAYDEN system (toggle position 1)
3) run the fans manually (toggle position 2).
This arrangement gives me the flexibility to run the system the way I want to –including full manual operation with either or both fans running all the time.
CREDIT-WHERE-CREDIT-IS-DUE: This is a very clever modification created by WILLE because it preserves the factory setup while allowing the driver to select a fan operation mode that suits the conditions. I’ve implemented this on my car (one of the few NON-FACTORY upgrades I’ve made to my car) and love the way it works. It’s a little challenging to install the 3647 switch if you want it to look factory, but once installed, it works SEEMLESSLY! Many thanks to WILLIE for this mod!
