In running the last week or two at the track it occurred to me that I would like to put in a cooling fan switch but In keeping with the stock tradition I knew that the Ac coming on was one criteria for the PCM turning the fan on. So upon trying to turn on the AC in the staging lanes (My AC is gone so this really would not help those with AC) I found that the fan still will not turn on.
In looking up the description and operation of the cooling fan I found that the line pressure switch on the high side (located on the small pipe coming from the condenser on pass side out of the same harness the coolant level switch is wired) has to register more than 30 psi and less than 392psi (0-5v on a reference scale) This means that simply jumpers from ground to signal (black to red and black) gives you a reading of less than 30psi. Jumper from the 5v reference (grey) to the red/black gives the high side of more than 392psi so neither work alone to kick on the fan.
Enter a 500ohm resistor.
Basically for those without AC looking for an easy way to manually control your cooling fan you can jumper with a 500ohm resistor from 5v reference (grey) to the signal which is the red/black. This can more cleanly done by hacking apart the sensor so you can simply plug it in and seal off the stock connector. Then all you have to do is hit the AC button and on comes the light, on comes the fan :-)
I will get some pictures tomorrow for you all to take a look at. I will also verify the wire colors and such too. MY plan is to hack apart the sensor and solder something permanent up so its sealed but still removable.
Anyone interested in this?? I would be more than happy to make a few of these as well if someone finds they would like one.
Buildin' n' Boostin for 08' - Alex Richards
i like it. i was trying this a month or 2 ago but gave up and did it the other way... i like this because you don't have to find place for another switch
exactly, and like I said, completely not messing with any or the harness or connectors or stock switches.
If anyone wants one of these pm me and I can give you my address and if you have a spare switch I can make a couple of these for cheap. Maybe $15 bucks shipped. plus your switch. Helps if its non working too...at least then its just a non working item.
Buildin' n' Boostin for 08' - Alex Richards
I'm confused... you said:
Quote:
Basically for those without AC looking for an easy way to manually control your cooling fan you can jumper with a 500ohm resistor from 5v reference (grey) to the signal which is the red/black. This can more cleanly done by hacking apart the sensor so you can simply plug it in and seal off the stock connector
And also said:
In looking up the description and operation of the cooling fan I found that the line pressure switch on the high side (located on the small pipe coming from the condenser
Quote:
But if we don't have AC (I don't), yes we could get the HVAC panel from an AC car and wire up that switch to control the fan, but we don't have a condenser so would we even have the sensor or wiring you are talking about, and is the ECU programmed to pay attention to a sensor that isn't there?
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<<<<<2003 Sunfire Sedan>>>>>
(apparently I don't know how to properly use the Quote button... or the preview button haha)
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its possible the car would still have the wiring for the sensor. alot of times the manufacturer will use one harness as the extra cost of there being wires for something that isnt in one particular model is easier than making 2 or 3 different harnesses. if not, you may be able to do weasels mod and wire it up to the AC button of an HVAC pannel with AC. this would still eliminate having to mount another switch some where else in the car.
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Adam Kappheim wrote:I'm confused
your confused becuase hes talking about people who have REMOVED their AC. theres no point in trying to do this if your car came without a/c. you might as well just do a switch
Alex Richards wrote:Enter a 500ohm resistor.
Basically for those without AC looking for an easy way to manually control your cooling fan you can jumper with a 500ohm resistor from 5v reference (grey) to the signal which is the red/black. This can more cleanly done by hacking apart the sensor so you can simply plug it in and seal off the stock connector. Then all you have to do is hit the AC button and on comes the light, on comes the fan :-)
Has this worked for you yet?
Because I'm guessing no.
The PCM is reading voltage output from the sensor, not currrent.
Jumping 500Ù from power to signal will give the same voltage as jumping 0Ù across them.
What you will probably need to do is make a voltage divider with 2 resistors. Use your 500Ù resistor from power to signal and use a second 500Ù resistor from signal to ground. This will cut the reference voltage in half that is going to the signal line (2.5v) and will make the PCM reading fall in the center of the sensors range.
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protomec wrote:Alex Richards wrote:Enter a 500ohm resistor.
Basically for those without AC looking for an easy way to manually control your cooling fan you can jumper with a 500ohm resistor from 5v reference (grey) to the signal which is the red/black. This can more cleanly done by hacking apart the sensor so you can simply plug it in and seal off the stock connector. Then all you have to do is hit the AC button and on comes the light, on comes the fan :-)
Has this worked for you yet?
Because I'm guessing no.
The PCM is reading voltage output from the sensor, not currrent.
Jumping 500Ù from power to signal will give the same voltage as jumping 0Ù across them.
What you will probably need to do is make a voltage divider with 2 resistors. Use your 500Ù resistor from power to signal and use a second 500Ù resistor from signal to ground. This will cut the reference voltage in half that is going to the signal line (2.5v) and will make the PCM reading fall in the center of the sensors range.
Yes it has worked for me and heres why...
The sensor is a piezoresistive PPC sensor. This means that as pressure changes resistance inside the sensor changes. The "PPC" designation stands for positive pressure coefficient In simple terms as pressure goes up so does the resistance. The 5v reference circuit is simply that, 5v goes into the sensor and passes through the full resistance of the sensor element all 5v is dropped across the resistance and grounds back to the battery via the pcm. This provides source voltage which must ground somewhere otherwise all 5v would simply drop across the resistance between the 5v reference and wherever the signal wire is at (basically it would give you a high resistance high pressure reading all the time) A third signal wire terminates at the piezoresistive element and essentially taps into part but not all of the total resistance of the sensor therfore resulting in your varied reading based on what the pressure is on the element itself.
So to make this work we first need to make a full circuit...we can either put a resistor between the 5v ref and ground....basically doing nothing but burning power...or we can go between the signal and ground...but we will also get nothing because no voltage is being applied to that circuit in the first place so in essence its not a circuit anyway. Instead we must take our 5v reference and drop some but not all of it across a resistance, Now why does this work? Because the PCM ALSO has a resistor inside the signal circuit to protect it if there is zero ohm load across 5v ref and signal. This also serves to help us in that the 500 ohm resistor will not drop all 5v across it, instead you must know the resistance of the pcm's internal protection circuit to know how much is actually dropped. But this is nonpoint to most anyway since theres no value to knowing that information.
I hope I explained this well enough...I can further explain if I need too...I did'nt get pictures today either...sorrry...
Buildin' n' Boostin for 08' - Alex Richards
Basically the PCM looks at voltage readings at the sensor....it does not care what 5v ref and gnd are doing...they are constant. ITs simply looking at how much voltage is being dropped before the protection circuit out of the 5v.
Buildin' n' Boostin for 08' - Alex Richards
