Aux Fan controller

[Minuit]

My truck's been running a little bit warm recently when sitting still, so I decided to check it out. Turns out my electric fan doesn't turn on at all by itself. The fan turns on when the engine temp sensor on the thermostat housing is unplugged, so the fan is in working order. I know the controller for the aux fan is somewhere on the radiator, but does anyone have a pic of where? Unfortunately my FSM is 120 miles away at the moment.

[HOrnbrod]

The aux fan is controlled by the ECU for the HOs. The radiator sensor is for Renix aux fan.

 

http://comancheclub.com/topic/48804-electric-cooling-fan-issue/?hl=aux+fan&do=findComment&comment=496745

[Minuit]

Oh, damn. I seem to remember the aux fan used to come on a lot more than it does now. This evening it didn't come on at a gauge indicated temp of ~225 F (only gets that hot when sitting. Believe my fan clutch to be dying) Way too hot for me to be comfortable. I really don't want to hack into any wiring but I may be wiring a manual switch for it later on.

[HOrnbrod]

~225* is about when my aux fan comes on w/o the A/C too. Also too hot for me, thus the switch. I've only had to use it a few times in the summer stuck in traffic.

[Minuit]

Oh, right. Forgot about the A/C. Still haven't charged that back up after my heater core replacement. Guess I could just turn the A/C on for a minute if it starts creeping up. Would keep the system from just sitting unused too...  :doh:

[gogmorgo]

With no refrigerant, the a/c won't come on. Don't know if it'll trigger the fan either if it's not on. But if it's cold enough out, the a/c won't come on anyhow as the pressure in the system drops low enough to trigger the safety switches. I can hear mine kicking on for a couple seconds every now and again when in defrost.

[Minuit]

With no refrigerant, the a/c won't come on. Don't know if it'll trigger the fan either if it's not on. But if it's cold enough out, the a/c won't come on anyhow as the pressure in the system drops low enough to trigger the safety switches. I can hear mine kicking on for a couple seconds every now and again when in defrost.

 

I know.  :thumbsup:  That's why I need to get it charged up soon.

 

Probably would be best if I just wired up a switch anyway. Now to figure out how to make it look factory.

[gogmorgo]

XJ rear wiper switch? Throw in some heavy resistors (say from a blower motor resistor pack) and make it a two-speed. Or just a defrost switch for single-speed.

[Minuit]

Exactly what I was thinking. I even have a spare XJ switch plate on hand. If I really wanted to get fancy I could stencil a graphic of a fan above the switch.

[Minuit]

Just to provide some closure, I wired up a switch in the cab (a factory fog light switch from the junkyard does the trick) to turn the fan on. All that's needed is a switched ground to a blue/pink wire (at least on a '91) corresponding to pin 31 on the ECU harness as given in Don's link above  :thumbsup: