relay and wiring weirdness

[Pete M]

The cooling fan in my Liberty has a hi fan relay and a low fan relay.  plug in one relay and the fan kicks on.  take it out and plug in the other, the fan kicks on.  plug both relays in at the same time and they both click and the fan dies.

 

any guesses?  short?  insufficient ground? 

[jdog]

I would suspect a bad fan tho

[Pete M]

one of the CRD guys on fb says his only fires one relay.    still waiting on confirmation of which one fires. 

[Ωhm]

Is KEY ON, KEY OFF or it doesn't matter?

[Pete M]

I'll go run some more tests.  so far I've only done: key on, engine off, AC button pushed, interior blower on.

[Pete M]

both relays are firing now regardless of AC or interior blower (key turned to on) and I'm assuming that's because I just got back and the engine is still warm.   Individually, both relays turn on low speed.

 

BUT, unlike earlier, now when I insert the second relay (doesn't matter which was first) the fan kick on high for a brief moment and then turns off. 

 

 

[Pete M]

the guy replied and the lo speed is activated by engine off and AC on. 

 

this makes sense to me.  AC gets low speed, engine heat gets hi speed.  no idea if I'm correct, but it makes sense to me.  

[Ωhm]

I wonder if the coolant temperature sensor for the fans have anything to do with this?

[Pete M]

tomorrow I'll take another crack at it with a cool engine and see what's going on.   

 

wouldn't shock me at all to find out there's a rubbed-bare wire somewhere.  these Jeeps are know for them.   

[mjeff87]

1 hour ago, Pete M said:

the guy replied and the lo speed is activated by engine off and AC on. 

 

this makes sense to me.  AC gets low speed, engine heat gets hi speed.  no idea if I'm correct, but it makes sense to me.  

 

That makes sense to me.  My KJ only has an electric fan (single), no mechanical.  It barely runs......I can idle it for 25 minutes and it won't turn on, unless I turn the AC on.  Weird.

[Pete M]

ok, so now it's doing the same thing all the time.  turn key with one relay in (either one) and the fan turns on Lo.  plug the other relay in and the fan bumps to Hi for a half second and then shuts down (both relays remain clicked on).  interior blower and AC button position mean nothing.

[gogmorgo]

Is there some sort of fan speed resistor pack? Just wondering how the fan motor distinguishes between high and low speed.

[Pete M]

finally found my multimeter! 

 

there are 2 power wires to the fan.   

 

Applying 12 volts direct from the batt to the one wire appears to give the same fan speed as applying 12 volts to the other wire. 

 

checking power at the plug:  plug in one relay and I get 12 volts through one wire, plug in the other and I get 12 volts through the other wire.  plug in both relays and I get 0 volts from anything.  so it appears that plugging in the second relay is causing both relays to shut off.

[mjeff87]

There is a fan relay, it's on the driver side inner frame rail, below the battery-ish.  Check it, it might be fubar'd.  I'll see if I can snap a pic on mine...BRB.

 

edit:. Here it is, at least on a gasser.  I can't imagine it would be different on an oil burner

 

 

[Pete M]

but it might be different on the later models.  I've got 2 fan relays in the engine bay fuse/relay center.

[Ωhm]

27 minutes ago, mjeff87 said:

edit:. Here it is, at least on a gasser.  I can't imagine it would be different on an oil burner

 

Could that be the Pulse Width Modulation (PWM) controller, if equipped.

[Pete M]

57 minutes ago, mjeff87 said:

There is a fan relay, it's on the driver side inner frame rail, below the battery-ish.  Check it, it might be fubar'd.  I'll see if I can snap a pic on mine...BRB.

 

edit:. Here it is, at least on a gasser.  I can't imagine it would be different on an oil burner

 

can you get the camera a bit closer and snag the part number?

[mjeff87]

[mjeff87]

Radiator fan relay.

[Pete M]

my quick research say your part number is for 02-03 KJs.  can't find anything like it in my 06.    does yours have relays in the engine bay fuse box? 

 

I think it's an early vs late change.

[Pete M]

I think my future holds me acquiring a replacement fan and wiring it in to a custom switch/relay. 

[mjeff87]

Could very well be an early model thing.  I've never had any issues with the fan (aside from it taking a LONG time to turn on) so I've never really studied the circutry much.  Which means "never".

[mjeff87]

From the little bit of internet sleuthing I've done on the CRD, the 2-speed fan is related to the A/C.  Apparently, the low speed circuit is energized when the A/C is engaged, and the high-speed is energized via engine temp input (around +230F for the 2.8, and +255F for the gassers).  Not sure that any of that is a clue, but I thought it was worth mentioning.  What happens when you plug both relays in and turn on the A/C?  You "should" get the low-speed to function, at least.

 

[Pete M]

low speed functions all the time (if only one of the relays is plugged in) and nothing happens if both relays are plugged in.    something is amiss in whoville. 

[Pete M]

not sure what it means, but I can insert one or the other of the relays (low speed activates) and then bypass the other relay with a paperclip and hi-speed activates just fine.  but if I slap the other relay in there, both relays shut down.