PWM cooling fan(s) control using ECM

[Denvervet]

If you have crimpers...should be able to just buy metripak or weatherpak connector and make your own harness. Waytek is one source for such items.

[mikels]

Originally Posted by Lous69

My thinking is that GM validated those modules for the current draw of just one C6 Corvette fan. Since I have two fans, it seems safest to use two modules vs. "hoping" one module will be able to handle the current draw of two fans.

No need for 2 fan control modules unless current demands from dual fans exceed capaicty for single module. I've run dual Spal fans from production Corvette fan module without issue (I will say that I have yet to ever use an aftermarket fan that comes close to performance of the factory designed and developed fans).

PWM output from ECM has to match what fan module is looking for. If you are using fan module from Corvette and match the calibrations in controller to a Corvette, will all work fine. 128 Hz is what Corvette fan controller is looking for.

Originally Posted by parsonsj

Just to clarify (for me, anyway ) : the E67 in the LSA crate motor offering from GM (pn 19259293) can monitor the A/C line pressure and turn on the fans? Does it do that with PWM support (just running the fan enough to keep the high side pressure to certain number)? Or does it do that by running the fans full speed until the high side pressure drops below a threshold?

And all the while, it's keeping track of the coolant temp and running the fans appropriately for that too?

Sweet!

Yes - AC pressure calibration just drives fan high enough to keep pressure within boundries set in cal. It's a table relating AC pressure in kPa to fan output %.

Fan duty cycle is controlled by 5 inputs: ECT (engine coolant temp), AC pressure, IAT (intake air temp), EOT (engine oil temo), TOT (trans oil temp). Highest request wins (in other words if AC pressure is requesting 50% DC and ECT is only 30%, 50% is what is commanded).

Most installations do not monitor oil temp (decrete input into ECM) and trans oil temp is either from descrete input of trans temp into ECM, or over CAN bus from TCM (transmission control module).

If you use PCS (Powertrain Control Systems) trans controller for automatic trans, trans oil temp (TOT) is broadcast over CAN messages and will work with crate engine controller kit to drive fan output.

Typically, ECT and AC will be primary drivers for fan DC - unless you have an unbalanced system from cooling perspective.

Dave

[Lous69]

Originally Posted by parsonsj

I'm glad I started reading this thread! Very very interesting, and far superior to what I did on my last project which was to use a relay to override and run the fans with pressure monitoring via a trinary switch.

Just to clarify (for me, anyway ) : the E67 in the LSA crate motor offering from GM (pn 19259293) can monitor the A/C line pressure and turn on the fans? Does it do that with PWM support (just running the fan enough to keep the high side pressure to certain number)? Or does it do that by running the fans full speed until the high side pressure drops below a threshold?

And all the while, it's keeping track of the coolant temp and running the fans appropriately for that too?

Sweet!

We are still trying to figure out how to handle integrating the Vintage A/C system cooling fan requirements into our overall cooling strategy. This is like that Whack-a-Mole game. Every time you think you have a handle on how to make everything place nice together something else pops up.

Oh well, that's what makes it fun right????

First let me remind you that today I am just a newbie trying to figure this all out for the first time. Dave, who thankfully has chimed in on this thread, has numerous successful installs under his belt including Stielow's latest cars so he is MUCH more credible than me. Bottom line, don't follow my lead until you see the final results. I will keep you posted as we learn.

Kevin and Trevor of V8TV are keeping me honest and out of trouble too.

Getting back to your questions about how the ECM requests cooling fan speeds and how we hope to integrate the Vintage Air system into our cooling fan strategy:

Here is what I have been able to find regarding how GM sets up the cooling strategy in the ECM for PWM control of cooling fans:

Engine coolant temp. strategy:
Cooling fan starts at approx. 204 Deg. F (at 10% duty cycle) and steadily increases with temp up to a max of 90% duty cycle (which they consider full on or high speed) at 235 Deg. F and higher.

A/C Pressure strategy:
Cooling fan starts when A/C pressure is approx. 160 psi and reaches high speed at 360 psi.

Engine Oil temp strategy:
Oil temps above approx. 302 Deg. F will trigger high speed fan on.

Transmission Oil temp strategy:
Trans oil temps above 270 Deg. F will trigger high speed fan on.

Vehicle shut off strategy:
If engine coolant temp at key off is greater than 235 Deg. F or the A/C pressure is greater than 249 psi, the cooling fan duty cycle is set to 50%. If the coolant temp drops below 230 Deg. F, and the A/C pressure drops below 241 psi, the fan will shut off. Otherwise, the fan will automatically shut off after 2 minutes regardless of temperatures.

When multiple cooling fan requests are received the ECM uses the highest cooling fan speed of all requests.

Now, according to Vintage Air,

We need to find out if the fan algorithms can be tuned to request full speed fans at 260 PSI instead of the GM setting of 360 PSI because if pressure in the Vintage Air system is allowed to go much higher than 275 psi, the ability of the system to absorb heat is greatly reduced.

Absent of that, they would be concerned that we will not have efficient cooling because the GM A/C strategy is designed for a fixed orifice tube expansion with a variable displacement compressor, as opposed to the thermostatic expansion valve system Vintage Air employs.

The Vintage air system does have an on/off cooling fan control. It calls for fans on at 254 psi and has a safety shutoff for the system at 406 psi in case there is a fan failure or a blockage develops in the system.

This means we need to check into a few things as follows:

1. We need to make sure that we can turn off the ECM algorithms for any temperature sensors we might not use without causing the ECM to get confused or angry with us. For instance, we do not presently plan to sense the trans. temp or the oil temp through the ECM even if those algorithms reside in our version of the E67 ECM. We only want to "turn on" the coolant and the A/C pressure algorithms that we believe/hope to be resident in the LSA crate motor E67 controller but "turned off".

2. We need to make sure we can reset or tune the A/C pressure settings to emulate the way the Vintage A/C system controls cooling fans.

3. We need to verify that we install the GM A/C pressure sensor in the correct location within the refrigeration circuit.

4. We need to think the whole strategy through again to see what we might be missing.

Of course, we may still need to fall back to a more conventional cooling fan strategy if this all proves undoable for some reason. It's always good to have a Plan B.

[parsonsj]

Lou, all this stuff is amazingly topical to me as well. I've got a good buddy (Jeff Tate, one of my fellow mods over at PT.com) who works the parts counter at a Chevy dealership near Atlanta. He can help source all the parts needed here: PWM module, fan, connectors, A/C sensor and connector, plus the pins needed to add the wires to the ECM connectors.

I follow the need to disable transmission oil and maybe engine oil temps from the algorithm, plus change the parameters from 360 psi to 260 psi on the pressure side of the refrigerant circuit. I'm now beginning to wonder about fan dimensions, and how it will fit in a 69 Camaro body. I'm not sure sure the difference between the V/A compressor and the GM matters that much... as long as the fans generate enough cooling to keep the high side pressure below 300ish psi.

Of a greater concern is that the ECM has no way to turn off the compressor. That's a function of the trinary switch -- which only passes on the compressor on request as long as the high side pressure is under 260 psi.

So another question would be: can the E67 be made to take in the compressor request from the dash switch, and only signal the compressor clutch to engage if the pressures are safe? And to withdraw that request if the pressures exceed a programmable threshold (say 325 psi)?

[mikels]

Originally Posted by parsonsj

Of a greater concern is that the ECM has no way to turn off the compressor. That's a function of the trinary switch -- which only passes on the compressor on request as long as the high side pressure is under 260 psi.

So another question would be: can the E67 be made to take in the compressor request from the dash switch, and only signal the compressor clutch to engage if the pressures are safe? And to withdraw that request if the pressures exceed a programmable threshold (say 325 psi)?

E67 can and does control compressor - in factory installations. Issue is it gets AC request from HVAC module over CAN bus. And I don't see anyone that is going to solve that puzzle anytime soon.

Best solution is to allow Vintage Air (or whatever) unit control compressor, and ECM control fans. Again, you can set fan DC based on AC pressure (which is why you need to install sensor in AC line and wire to ECM).

[parsonsj]

Originally Posted by Dave

E67 can and does control compressor - in factory installations. Issue is it gets AC request from HVAC module over CAN bus. And I don't see anyone that is going to solve that puzzle anytime soon.

Best solution is to allow Vintage Air (or whatever) unit control compressor, and ECM control fans. Again, you can set fan DC based on AC pressure (which is why you need to install sensor in AC line and wire to ECM).

Thanks again for all the insight and answers. I love this stuff!

If the V/A (or ISIS) controller manages the compressor, then there must be a sensor to know when to turn off the compressor when liquid side pressure gets too high. So we're back to a trinary switch (maybe just a binary switch?) to do that -- negating one of the key advantages of having the ECM manage the fan. I suppose it's still better for the ECM to manage the fan (does it soft-start the fan to reduce inrush?), but this hybrid system will have two pressure sensors that aren't integrated.

I'm going to talk to ISIS about their V/A controller and whether or not it can be modified to support the CAN-bus protocol to be able to talk to the ECM. I'm sure Jay's question will be: what is the CAN-bus sequence to tell the ECM to enable the A/C clutch?

Edit: I realize that just the CAN-bus electrical connection isn't enough. GM has a proprietary protocol that would have to be reverse-engineered to get this to work. I also asked ISIS about their ability to read CTS and A/C sensor data and manage the fans. I'll report back.

[samckitt]

Tried to read all of this, not all of it sunk in & now my head hurts. In a nutshell, can I use a vette fan & PWM module & hook it up to my GMPP LS3 controller kit with extra harness & retune the ECM to work with the PWM fan instead of just on/off?

[mikels]

Originally Posted by samckitt

Tried to read all of this, not all of it sunk in & now my head hurts. In a nutshell, can I use a vette fan & PWM module & hook it up to my GMPP LS3 controller kit with extra harness & retune the ECM to work with the PWM fan instead of just on/off?

Simple answer - yes

[Lous69]

Dave,

When my GM PWM fan modules arrive I am going to play with them on the test bench to learn more about how they work and respond to various input signals.

Thanks to you, I know I need to provide them with a 128 Hz PWM signal which will be no problem.

I can measure the impedence of the module when it arrives but I don't know how to determine what voltage range of PWM signal it will be looking for

Do you happen to know what voltage the module is looking for in the input signal it receives from the E67 ECM?

Thank you so much for your knowledge. You are the Man!

[mikels]

Originally Posted by Lous69

Do you happen to know what voltage the module is looking for in the input signal it receives from the E67 ECM?

ECM signal is switching to ground - not voltage.

Most output functions of ECM are that way: injectors, coils, etc. Ground signal is switched with power supplied directly to device.