2005 Elusive Fan Relay Module

[eric1514]

Interesting experiment this morning.

I disconnected the harness to the fan so I could probe it with test lights. With the engine on and the A/C on, the low speed side turned on the test light after about 10-15 secs and it remained on. About 2 mins later, the high speed side came on, presumably because the fan was disconnected. The point is, both circuits were energized simultaneously.

Secondly, I only have one test light, so I used my voltmeter so act as a second one. When the high speed side came on it read 14.6v. Just for fun, I read the low side. It also read 14.6v. Higher than I would have expected, but what do I know.

Eric

 

[eric1514]

Went to the junkyard. I found 2 3-wire fans. One was DOA like mine, but this time the high side was dead and one worked perfectly at both speeds but it was an aftermarket unit with the wrong connector on it and I didn't feel it was worth the trouble to splice on the correct one. I ended up ordering a TYC version.

 

[JeepJeepster]

Did some testing on my 2004 so I wasn't just guessing. I have a bi-directional scan tool so I can turn the fan on and off.

The low speed relay is indeed turned off when the high speed comes on. So on my 2004, turning both on would most likely burn out the windings. My 98 Grand Cherokee functions the same.

The PCM does some weird things. I didn't use a test light, so no load, but it shows +12v on the negative side of the relay coil with the relay in or out. It switches to a ground when you energize it.

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[eric1514]

That’s interesting. I wonder if the HD cooling you have acts differently than the non HD I have. I would think not, but I’m not as familiar with these things as you are. I do know both the hi and lo circuits to the fan on my truck were energized at the same time. Whether that’s right or not, I don’t know.

 

[JeepJeepster]

My KJ actually did not come with the HD cooling, but I added it later on. The electric fan is stock though, I didn't change it.

Some KJ's came with a single speed fan, but I think that changed in 2004. Maybe only the 02-03's with the HD cooling came with a single speed fan. I cant find a single speed fan in my 2004 FSM.

 

[eric1514]

I looked at around 7 KJs today at the junkyard(s) with the non HD cooling and only 2 had a 3 wire (2 speed) harness. It seems like 2004-5 are the only years. The 2007 I saw also had a 2-wire fan. I don’t know why they kept changing things.

 

[JeepJeepster]

People get bored and need to change things up to justify their job... That or they just figure out a cheaper way to build them haha

 

[eric1514]

I bought a new aftermarket fan (TYC brand) and installed it in my Liberty. Things seem to be working as they should. It's cold outside so the A/C kicks on and off and thus the fan doesn't come on immediately like I figured it would, but after the engine gets warm it comes on and runs until things cool down. That didn't use to happen so I'm claiming success. I imagine in the summer, things would act differently.

For posterity:

1) The TYC fan/shroud weighs about 2/3s of what the factory fan/shroud weighs. It probably won't last as long.

2) A fan with three wires on the connector will run when you hook up a battery to the center pin (-) and (+) to either of the other pins. One combination is high, the other is low.

Thanks everyone for your help. It's nice to have a sounding board when you're thinking out loud.