Skandocious
Post Whores Make Me Sick
So I've discovered a small bug in my fan circuit. The way I've got it wired is with a 3 position switch, as follows:
~top = automatic; turn on low-speed when temp probe reaches xxx degrees OR if I turn on the A/C
~middle = force everything off
~bottom = force high speed on
So let me lay out the scenario for when the bug rears its ugly little head. Driving around on a hot day with enough wind to keep the engine cool without fan; no a/c on either, so the fan is NOT running at this point. Pull up to a really long stop light and the engine temp climbs a bit -- normal -- hits a certain temp and the low speed turns on. All is good at this point EXCEPT that when the fan kicked on, I notice that the RPMs had a slight dip and then climbed back up. That's strange... The fan shouldn't mess with the engine RPMs-- did my compressor just turn on? Suddenly I notice that my vents are starting to blow ice cold air even though I'm on the VENT setting... Ehhh... WHAT?!
So clearly my fan circuit is backfeeding power into my truck's A/C circuit and turning on my compressor and accumulator (I tapped the power wire at the accumulator). I've only got 1 wire tapped in my A/C circuit so I know just exactly WHERE the power is backfeeding but I'm just trying to figure out how to fix it. My current circuit (which I designed) is shown below:
Right now I've got the third (center) relay there so that when the A/C kicks on, it will bypass my temp switch and send power to the inductive circuit on the low-speed relay, which will close the switch and send +12V out to the low speed windings on the fan. But it appears that when my A/C is OFF, and the temp switch gets closed, it's sending +12V backwards through the switched circuit on the center relay, and the switched circuit is already closed because there is already +12V going through the inductive circuit.
So I've already figured why it's happened, clearly the circuit design is at fault. But I've been through SO many different designs and I just don't think there's any other way to do this exactly the way I want while maintaining proper circuit protection. Would it be best to just put a diode on the wire that is backfeeding into the center relay's switched circuit?
~top = automatic; turn on low-speed when temp probe reaches xxx degrees OR if I turn on the A/C
~middle = force everything off
~bottom = force high speed on
So let me lay out the scenario for when the bug rears its ugly little head. Driving around on a hot day with enough wind to keep the engine cool without fan; no a/c on either, so the fan is NOT running at this point. Pull up to a really long stop light and the engine temp climbs a bit -- normal -- hits a certain temp and the low speed turns on. All is good at this point EXCEPT that when the fan kicked on, I notice that the RPMs had a slight dip and then climbed back up. That's strange... The fan shouldn't mess with the engine RPMs-- did my compressor just turn on? Suddenly I notice that my vents are starting to blow ice cold air even though I'm on the VENT setting... Ehhh... WHAT?!
So clearly my fan circuit is backfeeding power into my truck's A/C circuit and turning on my compressor and accumulator (I tapped the power wire at the accumulator). I've only got 1 wire tapped in my A/C circuit so I know just exactly WHERE the power is backfeeding but I'm just trying to figure out how to fix it. My current circuit (which I designed) is shown below:
Right now I've got the third (center) relay there so that when the A/C kicks on, it will bypass my temp switch and send power to the inductive circuit on the low-speed relay, which will close the switch and send +12V out to the low speed windings on the fan. But it appears that when my A/C is OFF, and the temp switch gets closed, it's sending +12V backwards through the switched circuit on the center relay, and the switched circuit is already closed because there is already +12V going through the inductive circuit.
So I've already figured why it's happened, clearly the circuit design is at fault. But I've been through SO many different designs and I just don't think there's any other way to do this exactly the way I want while maintaining proper circuit protection. Would it be best to just put a diode on the wire that is backfeeding into the center relay's switched circuit?
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Except I'd want it on the low speed not the high speed. I originally had it wired to the high speed and it was overkill. The low speed pulls TONS of air; the high speed pulls a ton of juice and so I only like using it in case of emergencies or under heavy load, like when I was running high RPMs at low speed for long periods of time on the snow trip.
