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Electric fan override question.

pipewrench

NAXJA Forum User
Location
GA
I have a 99 model that I recently deleted the A/C on. I've been reading lots of threads about making an electric fan override switch setup and had an idea I wanted some thoughts on.

Since I have no A/C, and the electric fan would run when A/C was on, can I jump out my low pressure switch and just turn the knob to A/C when I want the electric fan to run? Seemed logical, just thought I'd ask before jumping anything out. Thanks.
 
Well I went ahead and tried, jumped out LPCO and what I believe is HPCO...no dice. Tried each separate and then together.

Doesn't make sense to me, if the electric fan runs when A/C is running, how does it know I have it tricked?

The only thing that was strange to me was I couldn't measure any DC voltage at either switch, on either terminal to ground. Seems to me the controller would send out 12v, if it came back then the switch would be made.

I'd like to figure this out, it would be a nice mod for someone in my situation (No A/C anymore and would like to be able to run fan on demand)
1999 4.0 4x4 Automatic
 
I would tap into the e-fan wire and run a relay/switch to engage it when you want.
 
Well I could have sworn my fan came on with AC automatically, I must have been mistaken. After reading the first post it would make sense.

I have read the second post a few times already, I really doubt I'll ever put that much effort into it. It does look really good, but I probably won't find the time to go that deep. Thanks for the replies!
 
The AC/efan signal comes from the ECU - it's called the AC REQ line.

This may be "trapped" by other inputs to make sure the aircon is present and operating.

I'm not looking at wiring diagrams right now, or I'd see about "spoofing" that signal - or the high temp signal - to manually trigger the efan (it's easier on RENIX, since it's tripped by a logical OR circuit that has nothing to do with the ECU. Therefore, you can add a third "OR" path without endangering ECU solid-state circuitry with backfeeding.)
 
Well I could have sworn my fan came on with AC automatically, I must have been mistaken. After reading the first post it would make sense.

I have read the second post a few times already, I really doubt I'll ever put that much effort into it. It does look really good, but I probably won't find the time to go that deep. Thanks for the replies!

It seems to me that operation where AC on equaled Fan on changed in '99. After that the fan only ran on demand. I suspect that some engineer thought about it and figured why have the fan run if there is sufficient air flow already. Saves gas by not drawing extra on the alternator.

There are many ways of doing a fan bypass and there has to be atleast 3 that I have heard of. The thread DJ pointed to is just one.
Look at the bottom of this thread an the Forum did a quick search for you based on the thread title, those may yield a solution you want.

-Ron
 
The electric fan in my 96 and 98 will cycle on with AC or defrost mode selected, even at cold start.

Yeah - that's the programming that changed for 2000MY. A 2000 or 2001MY XJ 4.0 will only turn the fan on if coolant temperature gets to 220 or 230. Can't remember.
 
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