TunedPort350

I am replacing my single fan setup with a dual fan setup. I am of course going to add a relay for the second fan wired directly to the battery for the power to the fan.

My question is, what is the load rating for the ECM output which turns the single fan on? Can I just splice into the control portion of the existing relay to switch my new second relay, or will this be too much current draw through the ECM output?

I know from the factory GM had one fan controlled by the ECM and the other controlled by a thermo. switch in the pass. head. This is what made me think that maybe the output on the ECM couldn't handle the current for switching two relays.

Stuart Moss

Each relay draws ~200mA (0.2 amperes), so wiring two together will draw double that.

I see no problems with connecting both to the output of the ECM. But, at least in my 1991 Camaro, the ECM doesn't switch "on" until the temperature sensor reaches 222°F! That, IMO, is too high. I'd recommend using an aftermarket coolant fan switch (engine block) to come on at 200° or so (Summit has them). Unless you've got a reprogrammed PROM or??

However, you could always just connect the second relay's coil to be turned on by the contacts of the first relay. That way, there would be no additional load to the ECM.

I rarely need/use two fans simultaneously. Perhaps using a swtich to operate the second fan would be a good idea. Maybe using an on-off-on (center off) toggle switch (a very common item) would be a good idea. The center position would be "off" and one "on" position would be via the ECM (or ECM through the first relay switched contacts) and the second "on" position would be for manual fan operation.

[This message has been edited by Stuart Moss (edited June 14, 2001).]