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G Jiggy

Cooling Fans Running All The Time

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Anybody,

The cooling fans on my 2000 SVT are running all the time from cold start-up until I shut it down. The temp gauge reads normal (although it takes awhile to get there). At this point I have swapped out both the relays (high speed and low speed) with KGUs (known good units) and that didn't cure the problem. I heard somewhere (in the distant past) that the PCM controls the cooling fans, not a temp switch.

 

So I guess the question is: Is there a temp switch somewhere that controls the fans? If so, where? If not, is the PCM the culprit and does that need to be changed? If so, where is that? Sounds expensive . . .

 

Thanks.

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If the black wire with the white tracer from the A/C presure switch next to the overflow is grounded, the management system will run the fan(s) in high mode when the car is on. Insulation problem maybe, more plausable the switch is shorted. take off the connector and measure rsistance across the B/w and black terminals of the switch with engine off.... should not be continuity.

 

Gar

Edited by Gar

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THnaks for the quick reply Gar;

 

Well, here's what I've done so far. I pulled off the connector to the high pressure switch (it's right by the coolant overflow tank) and started the car. The fans didn't engage. I plugged the connector back in and the fans started. I pulled the connector off and the fans kept running.

 

The connector is a four wire design of: a black wire, a black with a blue trace, a green and a green with a red trace. Which two would I pick to measure resistance?

 

Steve

 

P.S.: I also took a look at your project pix. Very good use of a Duratec. Seems like such a natural.

 

If the black wire with the white tracer from the A/C presure switch next to the overflow is grounded, the management system will run the fan(s) in high mode when the car is on. Insulation problem maybe, more plausable the switch is shorted. take off the connector and measure rsistance across the B/w and black terminals of the switch with engine off.... should not be continuity.

 

Gar

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Steve,

 

Mine was older and used the black/black-white tracer. I think yours uses the black/black-blue. It's curious that the fans continued after pulling the plug, although I haven't looked all that deeply into all the logic. My quess is there's a delay (hysteresis) in the logic, and it would have turned the fans off in a little while (that is, of course, if the fault follows the therory). The pressure switch is normally open when the A/C is off. When the A/C is turned on, normal pressure builds in that line and the switch closes. Since using A/C increases the cooling task, the fans need to come on. This relationship of pressure indicating A/C on, is what the designers used for fan control.... they could have picked several different ways, this just happens to be the one they picked. The black wire of that pair is a ground.

 

The other switch in that same module is the "whow, pressure too high" monitor of the A/C system, although it's been a while since I looked at the diagrams to say I know which way it would read at the connector.

 

Gar

Edited by Gar

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You know Terry, when I read yours I said (eyes rolling, slap head) "Oh no, I can't be that stupid!!". But I may be, it was set at FLR/DEF. So, let's see . . . to answer you question.

 

So, with a cold morning start:

OFF- No fans running

PNL/FLR - No fans running

FLOOR - No fans running

FLR/DEF - Fans running (with A/C cycling)

DEF - Fans running (with A/C cycling)

PANEL - No fans running

A/C and MAX A/C - Fans running (with A/C cycling)

 

So that begs the question. My other cars I have/had do not run the fan/fans continually when the defrost is selected. I can understand full fan operation when full A/C is selected but where just the defrost is selected (with A/C in some sort of operation)? Is this normal for Fords or do I still have a problem?

 

Steve

 

With the heat/ position control inside the car in the 'OFF' position do the fans still run all the time?

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Steve,

 

I don't know about any of your previous cars, but any of mine (mostly all Ford products) all use the AC to help with drying the air any time any combination of defrost is used in addition to any time the AC is on.

 

In short, it sounds like your system is working fine, unless of course...I missed something.

 

 

Bob

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Well, I just feel damned foolish. Thanks for the help on this guys. I have to admit, my diagnostic skills sure have deteriorated with age. I'll go back into my hole now . . .

 

S

 

Correct,the AC does cycle in all but 2 setting to dry the air...

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Just be sure that the fans at BOTH low AND high speed work.With the control at 'OFF' again let the engine idle to temp,just over temp the LOW SPEED should kick in,then turn on AC and the fans should go from LOW to HIGH speed...

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Looks like I get one fan at full temp and the selector in the "OFF" position and the other fan kicks in with the A/C on. Seems normal to me. At least that's how my SAAB functions when the A/C is used.

 

Steve

 

 

Just be sure that the fans at BOTH low AND high speed work.With the control at 'OFF' again let the engine idle to temp,just over temp the LOW SPEED should kick in,then turn on AC and the fans should go from LOW to HIGH speed...

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