Lateral-g Forums - PWM cooling fan(s) control using ECM

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Quote:
Originally Posted by dontlifttoshift
We just did a Dominator in a 32 and we used a holley 500 PSI pressure transducer. This allowed us to skip the binary switch and the gm pressure sensor and do it with one sensor. We control the pwm fan and control compressor clutch engagement (high and low pressure cut off) through the ecm.

So far, it works. (End quote)

Originally I posted this under another topic, but thought it might fit better here.

I have a HP, not a Dominator, so maybe this won't work for me, also I am new at this so forgive me if I ask dumb questions. I have been pondering your solution and trying to figure out how you did this. I assume the 500PSI transducer is somehow plugged into the A/C line, presumably on the high side. The output from that transducer must somehow get into the ECU, (Inputs?), and set up to protect the A/C system in the event of too high or too low system pressure. Then is there a set point to turn on the fan, or speed it up, when the pressure reaches a particular threshold? Then is the cooling fan controlled by the ECU through a PWM for regular (or non-air conditioned) operation? If this is the set up, it would seem that some relays or diodes be necessary to prevent back feed of electricity.

Any assistance you can offer will be greatly appreciated.

Thanks, Larry

As an addendum, my '57 Chevy uses two Spal fans wired in both series and parallel, controlled by two temperature switches of different temperature values. At the lower temperature the fans come on wired in series, so they run at approximately alt speed. When the higher temperature is reached the fans which over to parallel wiring, therefore running at full speed. The trinary switch will override any operation or no operation of the fans and go to full RPM for the duration of what is commanded by the trinary switch. This system works well, but I do like the idea of a system that will keep the engine operating temperature more stable on a reduction of fan operation that is offered by using PWM. My Studebaker is still in the build up phase so it would not be that difficult to set it up with a PWM.

Yep, transducer goes in the high side and becomes an input.

The wire that runs from your AC controls to the compressor also becomes an input.

Then a wire runs from the ECU to the compressor, that is an output. Also need an output from the ECU to the C6 pwm fan controller.

The output to the compressor will not run unless it sees 12v in from AC controls _and_ pressure is between 30 and 400 psi, matching Vintage Air's cutoff on their trinary.

The fan control side has been covered in this thread already.

The problem you may have with the HP is limited number of I/O available.

Many thanks. So far I have I have not used any of the input/outputs of my HP ECU, so hopefully I will have enough. What method did you use to tap into the A/C line to mount the 500psi transducer?

We machined an 1/8" npt bung and welded it into a fitting near the drier. There may be a more elegant solution than that, I never bothered to look.

Quote:

Originally Posted by Larry R (Post 657454)

Many thanks. So far I have I have not used any of the input/outputs of my HP ECU, so hopefully I will have enough. What method did you use to tap into the A/C line to mount the 500psi transducer?

Got these at the junk yard, gave one to friend, he soldered/braized it onto the AC line, worked perfectly.

I think I paid $5 a piece for the connector pigtail, sensor, & segment of hose.

http://i242.photobucket.com/albums/f...04653_edit.jpg

Right, for the GM pressure sensor that is one way to do it.

The Holley sensor is 1/8" npt.

Quote:

Originally Posted by andrewb70 (Post 645029)

The information below is for a Holley HP or Dominator system, but I thought it would be handy to post it here.

So recently a buddy of mine presented me with a challenge. He has a street car that uses a Dominator ECU and he is using the C6 fan controller, just like I am. However, his car has A/C and he wanted to have the fan turn on at a predefined duty cycle whenever the A/C kicks on. I also know that some of you have the desire to be able to toggle the fan to full speed while at the track, and with the configuration that I previously posted, this is not possible. There may be other ways to do this, but this is what I came up with and it seems to work very well. I am testing it with a manual trigger through a virtual switch on my Holley 7" dash, but any switch will work, including a A/C compressor trigger.

First you need to create an Input and assign it to a pin (hopefully y'all know how to do that already). In my case I created a 20v sensor, but I see no reason why creating a 5v sensor wouldn't work either...

http://www.pro-touring.com/~andrewb/hefi/IO.jpg

Then you have to configure the sensor. I chose the Custom 20v from the dropdown menu and gave the sensor a minimum value of 0 and a max of 1. Essentially what I am doing is creating a binary switch. The reason for doing this is that simple 12+ or Ground triggers are not selectable in the PWM table, but custom sensors are!

http://www.pro-touring.com/~andrewb/hefi/sensor1.JPG

Here is the bottom of the screen...On the bottom scale, half the values are given a value of zero and the rest ramps up from 10-20v. Then I configure voltage values of zero to be zero and voltage values above 10v to have a value of 1.

http://www.pro-touring.com/~andrewb/hefi/sensor2.JPG

Now we can move to the PWM output screen and configure it. The Y-axis remains CTS but instead of having MPH on the X-axis, as I used to have, now I select the new A/C sensor that I created. The resulting table looks like this:

http://www.pro-touring.com/~andrewb/hefi/PWM2.JPG

This essentially splits the PWM table into to different conditions and they function independently, based on whether the trigger we created is ON (value 1) or OFF (value 0)...This set-up should work just fine for anyone that wants to turn their fan on at the drag strip...but it creates a different situation if you want the fan on when the A/C is on. With this configuration, even at highway speeds, the fan will be running at 50% (or whatever we assign to the cell of value 1 on the X-axis), which isn't really needed or desirable. In order to fix this, I have created conditional sensor triggers that will activate the PWM table.

http://www.pro-touring.com/~andrewb/hefi/triggers.JPG

I have set MPH as a trigger and set it to activate the table at speeds below 30 mph, and I also set the table to activate when temperatures are above 200 degrees. So in my friends case, with the A/C ON the fan will operate at 50% while at speeds below 30mph. Above that speed the fan is OFF, even when the A/C ON, however, if the CTS goes above 200 degrees, the table PWM table is activated again. Also keep in mind that the whole left side of the PWM table can have different values in all the cells. So you can have a minimum of 50%, but if CTS starts climbing, higher fan speeds can be commended.

With the A/C OFF, again, the right side of the PWM table is activated below 30 mph (this of course can be changed) or when the CTS goes above 200 degrees (this too can be changed).

This configuration should work for different set-ups and scenarios but the trigger values will have to be tuned to your particular combinations. This is due to variance in fans, hoods, thermostats, etc....

Any and all comments are welcome...

Andrew

I am trying to replicate or at least to use what you created here for my car. I cannot get the LH column on the calibration table to accept the number 1 as you have in your post. Also you will note it says "A/C (x10)" but I did not put that in so I do not know where that came from. Any help you can offer will be appreciated. Larry

http://i563.photobucket.com/albums/s...cu%20graph.jpg

http://i563.photobucket.com/albums/s...0graph%201.jpg

The input needs to be "custom 20v" not custom 5v.

Andrew

You actually don't have to do any of this if you have a linear AC pressure sensor. You can just create a AC pressure input and use it and coolant temp as your two axes of the PWM table. You can also add logic to turn the fan off above a certain speed and turn the fans on again if AC pressure or coolant temp rise, regardless of how fast you're moving.

What I showed is better suited for a system where there is no pressure sensor in the AC, but there is an input to the ECU to let it know that the compressor is ON.

Andrew

Ok, Thanks. I assumed since I am using a linear pressure sensor that is 5 volts that I needed to have the value at 5 volts; I will set it at 20 volts. I would like to have my dual Spal fans run through the PWM, (I have the Ford version PWM), but be able to have the fan run a little faster when the A/C pressure rises to values near to what a trinary switch does.

This forum has been very enlightening for me, thanks to you and others. Larry