Leverhead
Forum Newbie
Posts: 37
Loc: New Mexico
Reg: 02-05-11
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08-14-12 04:27 PM - Post#2259285
Hi all. I'm using the basic I/O and the 8 pin in/out connector (ground switched) to control my 2 fans. Has anyone done this in tandem with a manual switch (jumper to ground), say mounted on the dash? Holley tech says if jumped to ground manually to control the fans, voltage can be backfed into the ecu.
Also, i have a fan relay kit with 2 resistor suppressed (680 ohm) weatherpack relays. I know these are not sensitive to polatiry issues like a diode would be but are they sufficient to protect the ecu from flyback when the ground switch (via ECU) is disconnected?
Thanks in advance.
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mike beck
Contributor
Posts: 218
Reg: 05-20-10
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08-14-12 07:09 PM - Post#2259355
In response to Leverhead
What do you plan on doing? Wiring +12 to one side of the relay coil and using the ECM to provide the ground path? You also want to have a toggle switch in parallel with the ECM output so you can manually run the fans?
I prefer to let the ECM supply the +12 for the relay and have a constant ground on it. This way the resistor or diode can clamp the spike and the ECM should be out of the circuit.
Not saying your way won't work, I just have never wired them that way.
Those relays would be fine. The voltage spike coming back from the relay coil is not very big and very short in duration, the resistor would be fine.
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Leverhead
Forum Newbie
Posts: 37
Loc: New Mexico
Reg: 02-05-11
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08-14-12 07:53 PM - Post#2259385
In response to mike beck
Yes....I already have everything wired in...the ECU provides the ground switch. Before the Holley set up (Fast EZ EFI) the fan was ground switched thru the thermostat switch on the engine block with the manual override switch under the dash. I was inquiring about also having the manual switch to override the ECU...if it was possible or a no no with ECU controlled fans. Thanks.
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Danny Cabral
Member
Posts: 3161
Loc: Ellington, CT
Reg: 11-03-04
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08-15-12 12:21 AM - Post#2259463
In response to Leverhead
I was inquiring about also having the manual switch to override the ECU...if it was possible or a no-no with ECU controlled fans.
You simply need a diode on the ECU's fan signal wire. Shrink tube installation.
The relay trigger (coil) is very low amperage, so this diode will work well:
http://www.radioshack.com/product/index.jsp?produc...
May God's Grace Bless You
'78 BRONCO: 508" stroker, TFS heads, Dominator MPFI & DIS, A/C, Lentech Strip Terminator AOD, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim-over steering, 4" lift, 35" tires |
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