Fan wiring
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Teching In
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Fan wiring I'm swapping a 99 ls1 into my 67 nova. I have an American Autowire chassis harness and a painless ls1 harness. I'm running a PRC radiator with a single 16" spal fan (single speed). Can someone help a guy like me that's very new to wiring figure out how to wire a fan/relay for this setup? I already had the computer reflashed (VATS and emissions deleted) but I would still like to get the signal from the computer to turn the fan on and off. I need some type of diagram, what type of relay and what wire from the pcm to use as my switch. Thanks in advance, I'm sure i'll have many more amateur questions very soon.
Joined: Nov 2003
Posts: 11,329
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From: Jacksonville, FL (originally from Toronto Canada)
The f-body PCM controls two fans through three relays to provide low speed and high speed output. It does this by running the two fans in series for low speed (voltage available at each fan is half) and running the two fans in parallel for high speed (both fans get full voltage).
Unless the particular model fan you bought has some unusual configuration, it is not limited to a single speed. The electric motor will turn the fan at different speeds depending on the available voltage. So it is possible to wire it in a way that takes advantage of the dual speed control from the PCM by simply adding resistance to the low speed connection to simulate two fans in series.
To wire it for single speed use (i.e. it's either on or off), use a standard Bosch-style automotive relay and connect the relay coil ground wire to pin 42 of the PCM's blue connector (originally a dark green wire).
Unless the particular model fan you bought has some unusual configuration, it is not limited to a single speed. The electric motor will turn the fan at different speeds depending on the available voltage. So it is possible to wire it in a way that takes advantage of the dual speed control from the PCM by simply adding resistance to the low speed connection to simulate two fans in series.
To wire it for single speed use (i.e. it's either on or off), use a standard Bosch-style automotive relay and connect the relay coil ground wire to pin 42 of the PCM's blue connector (originally a dark green wire).
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Thank you, that's exactly what I needed to know. I thought I read somewhere when I looked my fan up that it was a single speed so I didn't know if reduced voltage would be harder on the motor.
What would you recommend to wire it up utilizing a low and high speed. I like the idea of doing that if I can without damage because I don't think it would cycle the fan nearly as much if it had a low speed since I'm not going to run a/c just yet.
What would you recommend to wire it up utilizing a low and high speed. I like the idea of doing that if I can without damage because I don't think it would cycle the fan nearly as much if it had a low speed since I'm not going to run a/c just yet.
Joined: Nov 2003
Posts: 11,329
Likes: 346
From: Jacksonville, FL (originally from Toronto Canada)
To set up two speed fans, you'll need two relays and a resistor. You can measure the resistance of the fan motor and get a resistor close to the same value so that low speed will be half of high speed. Or you could get a variable resistor (rheostat) that will allow you to adjust the low speed. In either case you're going to want to get resistors / rheostat that can handle 20 amps. I think the least expensive option would be to get an old style headlight switch from any auto parts store (the kind that pulls out for on/off and rotates for dimming the dash lights).
Wire the rheostat into the power feed going from relay #1 to the fan. Then wire a second relay with power output going directly to the fan (bypassing the rheostat). Connect the relay coil ground of the second relay to pin 33 of the red PCM connector (originally a dark blue wire)... that's the factory high speed fan control.
When the first relay is triggered by the PCM, voltage to the fan will be reduced by the rheostat making it run at a slower speed. When the temperature rises and the second relay is triggered by the PCM, full voltage will go to the fan making it run at full speed.
Wire the rheostat into the power feed going from relay #1 to the fan. Then wire a second relay with power output going directly to the fan (bypassing the rheostat). Connect the relay coil ground of the second relay to pin 33 of the red PCM connector (originally a dark blue wire)... that's the factory high speed fan control.
When the first relay is triggered by the PCM, voltage to the fan will be reduced by the rheostat making it run at a slower speed. When the temperature rises and the second relay is triggered by the PCM, full voltage will go to the fan making it run at full speed.
