PWM cooling fan(s) control using ECM

[Terrydmorgan]

I'm new to this forum, but I've been working on a couple pro-touring type Camaros for about 6 years. I'm on Pro-touring.com, but I haven't been active on this site, just lurking. I really appreciate the effort that went into this thread. This is an elegant implementation of a PWM controller for the cooling fans. I've ordered all the necessary items and will have mine hooked up soon too. Thanks for all the info.

I'm wondering if we could extend this solution to get rid of the binary switch in a Vintage Air system and let the ECM control the Sandeen compressor too. As I understand it, the function of the binary switch is to protect the compressor. That is, if the AC pressure is too high, the binary switch interrupts electric power from being delivered to the compressor clutch. Likewise, the binary switch will also turn off electric power to the AC clutch if AC pressure is too low. It seems logical that GM would implement a similar safety feature in their cars. And, since the AC pressure sensor is coupled to the ECM, it would seem likely that this binary type safety feature would be implemented in the ECM. Thus, I'd expect that there's a software routine in the ECM that uses high or low AC pressure to turn off the AC compressor clutch, and we might be able to modify this routine to use pressures that correspond to the Sandeen compressor instead of a production compressor. Moreover, I'd heard that GM's ECMs turn off the AC clutch if WOT or high RPMs is detected. The same routine may handle these functions too. These would be features I'd like to have implemented in my cars too.
I'm not highly experienced with ECMs and their software or with AC systems. I'm just trying to think about this logically. So, feel free to tell me I'm all wet, and/or point me to some materials that would help move this matter forward.

[mikels]

Originally Posted by Terrydmorgan

I'm new to this forum, but I've been working on a couple pro-touring type Camaros for about 6 years. I'm on Pro-touring.com, but I haven't been active on this site, just lurking. I really appreciate the effort that went into this thread. This is an elegant implementation of a PWM controller for the cooling fans. I've ordered all the necessary items and will have mine hooked up soon too. Thanks for all the info.

I'm wondering if we could extend this solution to get rid of the binary switch in a Vintage Air system and let the ECM control the Sandeen compressor too. As I understand it, the function of the binary switch is to protect the compressor. That is, if the AC pressure is too high, the binary switch interrupts electric power from being delivered to the compressor clutch. Likewise, the binary switch will also turn off electric power to the AC clutch if AC pressure is too low. It seems logical that GM would implement a similar safety feature in their cars. And, since the AC pressure sensor is coupled to the ECM, it would seem likely that this binary type safety feature would be implemented in the ECM. Thus, I'd expect that there's a software routine in the ECM that uses high or low AC pressure to turn off the AC compressor clutch, and we might be able to modify this routine to use pressures that correspond to the Sandeen compressor instead of a production compressor. Moreover, I'd heard that GM's ECMs turn off the AC clutch if WOT or high RPMs is detected. The same routine may handle these functions too. These would be features I'd like to have implemented in my cars too.
I'm not highly experienced with ECMs and their software or with AC systems. I'm just trying to think about this logically. So, feel free to tell me I'm all wet, and/or point me to some materials that would help move this matter forward.

You are correct in that GM ECM's do control AC compressor - however - GM ECM's receive AC compressor request signal over LAN from BCM (no discrete AC compressor request input directly to ECM).

So best solution I've come up with is AC pressure sensor into ECM to control fan output based on AC pressure - then use Vintage Air trinary switch to control compressor.

At least this way you can control fan output from coolant temp, oil temp, trans temp, intake air temp and AC pressure.

Dave

[Terrydmorgan]

Dave,
Thanks for the reply. I see, so if the ECM never receives an AC compressor request, then I assume the output signal from the ECM remains high all the time (i.e., the output is never pulled low by a real AC compressor request from the BCM)? Is there a way to permanently tie the AC compressor input request to simulate a constant request for AC from the BCM?
Terry

Originally Posted by mikels

You are correct in that GM ECM's do control AC compressor - however - GM ECM's receive AC compressor request signal over LAN from BCM (no discrete AC compressor request input directly to ECM).

So best solution I've come up with is AC pressure sensor into ECM to control fan output based on AC pressure - then use Vintage Air trinary switch to control compressor.

At least this way you can control fan output from coolant temp, oil temp, trans temp, intake air temp and AC pressure.

Dave

[samckitt]

After much searching, I have finally found a supplier for the PWM module connector body & terminals. So soon these will be in my hands:

[parsonsj]

Originally Posted by Scot

After much searching, I have finally found a supplier for the PWM module connector body & terminals. So soon these will be in my hands

Can you tell us more about this supplier?

[samckitt]

I can't give out all secretes yet. But they supply them to the car manufactures. I bought 5 of them. Don't need all of them, so i will have some extras for sale.

[andrewb70]

Scot,

Is this top secret information? LOL

Andrew