Radiator fan vs battery voltage

Hello everyone,
A couple dumb questions for anyone that has a voltmeter installed on their car. I've been messing with the dreaded cooling system fan for a while now, and just noticed something very interesting.

When my cooling fan kicks on low, the voltage drops from normal 14.xx to a solid 12. Rev the engine and it stays solid at 12 until the fan turns off. Almost like the low speed is putting a huge load on the system.
Funny thing is, if I manually turn the fan on high (I wired in an emergency relay), voltage will maintain 14. Neither circuit pulls the engine down abnormally.

So questions are:
1. What voltages are you seeing with low speed fan on at idle in gear?
2. Does the high speed consist of both motor circuits being energized at the same time? Not enough info in the ircm schematic.

I did a search but didn't quite come up with the answers.

I've done all of the preliminary checks, grounds, koeo, fresh alternator, good battery, power cables. Might be due to my crank UD pulley. All others are stock.

Thanks,
JJ

You are probably doing something wrong. The fan is a dual winding, and both should never be engaged at the same time. Furthermore, due to the high current design of the high speed winding, it should never be engaged from a standstill. The OE system is designed specifically to never turn on the high speed fan unless the low speed was already running first, and that the low speed fan is turned OFF before the high speed engages.

The high speed fan winding definitely draws more current than the low speed, and if you engage both at the same time the fan will actually slow down (well it will run at a speed partway between low and high so it could speed up slightly or slow down slightly depending on which speed was engaged first) AND it will also draw more current as the two windings fight each other. If you turn on the high speed fan without the fan already being in motion, the winding will initially act like a direct short circuit and will tend to blow fuses and will eventually burn up the fan motor (the same goes for running both speeds at the same time).

Yes I have been going through my car lately and undoing a lot of stupid things I did to it as a teen. I still want to keep the back up relay for insurance. Recently while checking out the system is when I noticed the voltage drop.


I'm still using the oem connector and ircm, the system is just supplemented by an additional relay tapped into the high speed circuit downstream of the ircm.

Thinking about energy management, wondering if any aftermarket vendors have made automotive brushless fan motors yet, that would be slick.

I did modify the motor wiring (this is where I tapped additional power), and I remember the 2 black wires were run in a way that was confusing to me at the time. Does anybody have a pic of an original early model fan motor connector?

My Haynes manual only shows 1 black for ground, 1 brown/yellow for low, 1 brown/orange for high. But my motor has 2 black. I'm sure they're both grounds, can anyone confirm?

JJ

Instead of bumping, here's an update: electrical system is checking out normal. Turns out I'm having similar issues as many others, low and high speeds are working however the low speed is turning on late. Not till about 225-230 confirmed with a lazer thermometer. New ecm coolant temp sensor, system purged of air, clean grounds. 185 thermostat is installed.

Planning to install a standalone fan control. Will update results.