Topic: have electric fan with temp control, how do i wire manual switch bypass

[bestos]

hey all,

I have been all over internet.  how do i take my simple 50AMP relay circuit and complicate it, so that I can use a switch in the cab of the jeep in order to override the temp sensor control (for driving on beach or sitting in extended traffic)

30-87 --> lincoln fan with circuit breaker
85-86 --> temp sensor to 12V ignition circuit

do i have to add another relay in order to bypass the temp sensor?

[bestos]

will this work??? i think so.  will use the normally closed section of relay make it either / or

[jfrabat]

First of all, I strongly recommend an override switch...  I have had 2 controllers fail on me, and the override is what has kept me going.  It is also best to use the override when trail riding (at least that is my experience).  As for the wiring, I use a 3 position switch, and the switch sends power to 2 relays, each of which allows power to reach either the control box (connected to the high speed side of the fan) or the low speed side of the fan directly, but never both at the same time.

[sharpxmen]

you don't need a second relay, just use a switch to bypass the thermocouple, it will close the main relay and activate the fan.

[Jeffy]

If you use 87A and 87 every time it turns on both are going to be powered which means the TEMP is going to be bypassed.  I'd put the switch on the key +12v and not on the battery +12v as well.

Like Sharp said, you don't need the second relay.

[jfrabat]

you don't need a second relay, just use a switch to bypass the thermocouple, it will close the main relay and activate the fan.

I did not get that one; if you use only one relay, it's then going to be either on by the control box, or forced on, but it cannot be turned off, right?

[sharpxmen]

the thermocouple (or thermo-switch) is just that, a switch activated at a certain temp, you put a manual switch in parallel with the temp controlled one and when you close it it will activate the relay, you flip it to off and will stop.
if you want an over-ride (so you can turn it off and it won't start at all) you can put a switch in series with the thermocouple, when closed (on) will activate based on temp, when open (off) will not turn on at all.

[Jeffy]

Ok, I get what he's trying to do now...

I would also move the temp to the other side of the relay.  It's on the power side and shouldn't be.  Most thermo switches can't handle a lot of amps.  No more then 35amps.  If he's wanting a master switch to be able to bypass the thermo switch then he'd need to add a DPDT switch at the key +12v and run a parallel line to the relay.  That would give him an ON/OFF/THERMO combination he's looking for.  Probably good to add some diodes between the bypass and after the thermo.

I don't have a ON on mine since there's never really a situation when I need it on.  If the thermo switch somehow breaks I can easily bypass it at the relay by switching some wires around.  They're all on plugs and next to each other.  I also have my A/C bypassing the thermo switch and turning on the fan when the clutch turns on.

[sharpxmen]

you're right, most thermo switches are on ther ground side, but the amps are the same regardless of which side of the solenoid he's wiring it (on the +12v keyed or the ground side).
I don't see the need for diodes, it's all series or parallel to the thermo sw, there's no backfeed into the +12v keyed circuit unless he brings in a permanent 12v wiring but i don't see the point of that

[bestos]

at my fuse box, there is only 1 switched and 1 fixed source - it saves a few crimps connections i think.  trying to use the fuse box and save some wiring, but the extra relay is still annoying.  will probably just figure a bypass switch in the cabin.

the temp switch amperage doesnt change regardless of 86 side or 85 side.  i tried to be cool and make it spiffy and its really not necessary