Thermo Switch and electric fan problems

[waezsn]

Im basically wiring an electric fan which is trigger by a ground going to a relay. Heres the problem. My thermo switch is triggered by a 12v wire. 3 prong switch.. one 12v.. one low.. one high. Is this normal or did someone do some weird hack job and wired my car the wrong way? I was going to tap the trigger ground relay wire to my low speed. But its giving a 12v instead of ground when it reaches operating temp. I am running a 318 switch. Any ideas?

[spdracrm3]

relay should have 4 wires power in (batt or key on) ,power out to fan , and two control wire (one being power the other ground ,with both the relay will close and switch the power to the fan motor) so you can permanently ground one side of the control for relay and have the coolant switch provide the power to the other relay control terminal and that will work just fine you can pick which temp the relay comes on at by which output from the coolant temp switch you use!

[waezsn]

I don't get it. I have 1 constant power.. one ignition power... one power wire that goes to the fan... and then a ground wire that triggers the relay. If I permanently ground that wire the fan is just going to constantly run. I don't have two control wires.

[waezsn]

Do you have a diagram you can show me so I can rewire it? Im kind of new to this relay thing.

[spdracrm3]

ok a relay is basically an electronic switch , it uses a low current control to switch a high current supply (ie a fan draws high current that would damage a normal switch) so a relay is used. a standard bosch 4 pin relay has pins # 30, 87 ,85 ,86 .

85 and 86 are the low current control side of the relay ,pins 30 and 87 are the high current controlled switched side of the relay. to activate the switching of the relay you need 12v power and a ground (it does not matter which of the two pins 86 or 85 each go to ) but as long as you have both the relay will work . so instead of controlling the relay by switching the ground side ,control it by switching the power side (using the 12v power you are getting from the cooling fan temp switch). so as stated run one wire from a ground to pin 85 or 86 , then run a wire from which ever 12v switched output from the cooling fan temp switch to the other pin 85 or 86 you didnt ground , now when coolant reaches switching temp it will supply power to relay and switch the high current supply to run the fan .

http://www.autoshop101.com/forms/hweb2.pdf

BTW you need to decide how you supply the fan power to the high current pin 30 , if you just run it to a 12v source that has power even when key is off the ,fan will stay running after you turn off ign key until the temp switch turns off due to coolant temp dropping below switch point ,this can drain the battery down . if you supply power from a switched supply thru the ign switch it will shut down fan as soon as key is turned off and not continue running.

[jlevie]

Understand that when using that switch to control an electrical fan you have to get a bit fancier or dedicate that switch to the control of the fan and loose the aux fan functionality.The low temp switch doses when the temperature is high enough, but it opens if the temperature get's high enough to trip the high temperature switch. A pair of relays in parallel, each of which is controlled by one of the signals, which in turn control the fan relay will allow the fan to run regardless of which is closed. Or you can disconnect the switch and wire the high & low contacts together and use that to control the fan.

[spdracrm3]

Understand that when using that switch to control an electrical fan you have to get a bit fancier or dedicate that switch to the control of the fan and loose the aux fan functionality.The low temp switch doses when the temperature is high enough, but it opens if the temperature get's high enough to trip the high temperature switch. A pair of relays in parallel, each of which is controlled by one of the signals, which in turn control the fan relay will allow the fan to run regardless of which is closed. Or you can disconnect the switch and wire the high & low contacts together and use that to control the fan.

what? dont see that on any diagram for the dual temperature fan switches, it shows one closed above 190F and second closed above 210F and have never seen them open above the set temp? both relay's will be on if temp is above 210F and the voltage will take the path of least resistance of the the un-resistored high speed circuit (not using the low speed as it has the resistor in the circuit) this is how the factory Aux fan is set up ,and as soon as high speed shuts off with the temp dropping below 210F its stays running on the low speed indicating it has not opened the 190F switch .
and no reason to stop using Aux fan as it will not be affected but using the dual temp fan switch to run/control another fan thru a separate relay(remember your only using low current to control the relay and the dual temp switch can certainly control multiple relays on each circuit).