Make E-Fan kick on when A/C is on P59 PCM?

[CDeeZ]

I ditched the mechanical fan on my daily driver 2004 Sierra a while back and I replaced it with an electric fan. I used a Taurus or MK VII??? style fan. I initially used this style fan on my turbo LQ4 truck. Since it works so well there, I just started using the Taurus fan on everything else.


Anyways, I have the PCM controlling the fan just fine, I made my own wiring harness and use a monster 125A relay even though it's surely overkill.

What I would like to do, is make the PCM kick the fan on when the A/C is on. So far, everything I have tried doesn't work. I have read mixed and scattered information about what needs to be done to accomplish this but I'm not sure what is true or pertinent to this application????

If I have to keep using a toggle switch to force the fan on during A/C months, no big deal I guess. Sure would be nice to make the PCM control the fan when A/C is on.


Side note, I run R152A aka electronics duster in my A/C and it works very well. I feel it performs better than R134A. Not to mention it's cheaper and probably better for the environment than R134A is......

[horsepowerguru427]

post the tune

[SiriusC1024]

Tie in to the compressor harness?

[Alvin]

I ditched the mechanical fan on my daily driver 2004 Sierra a while back and I replaced it with an electric fan. I used a Taurus or MK VII??? style fan. I initially used this style fan on my turbo LQ4 truck. Since it works so well there, I just started using the Taurus fan on everything else.


Anyways, I have the PCM controlling the fan just fine, I made my own wiring harness and use a monster 125A relay even though it's surely overkill.

What I would like to do, is make the PCM kick the fan on when the A/C is on. So far, everything I have tried doesn't work. I have read mixed and scattered information about what needs to be done to accomplish this but I'm not sure what is true or pertinent to this application????

If I have to keep using a toggle switch to force the fan on during A/C months, no big deal I guess. Sure would be nice to make the PCM control the fan when A/C is on.


Side note, I run R152A aka electronics duster in my A/C and it works very well. I feel it performs better than R134A. Not to mention it's cheaper and probably better for the environment than R134A is......

That truck should have a AC pressure sensor and so you should be able to copy all of the fan settings out of a truck that came with efans.. By 05+ most 1500's had them if you look in the repository.


If you don't have a AC pressure sensor. I sell a "A/C Bump circuit" It takes a input from the compressor and mixes it with ECM's fan controls to mix in fan control with the A/C being on. If the fans are on low and A/C is turned on the fans go to high, If the fans are off and A/C is turned on the fans go to low.. Etc.

https://www.pcmofnc.com/product/hot-...-bump-circuit/

[SiriusC1024]

That's a nice part.

[CDeeZ]

That truck should have a AC pressure sensor and so you should be able to copy all of the fan settings out of a truck that came with efans.. By 05+ most 1500's had them if you look in the repository.


If you don't have a AC pressure sensor. I sell a "A/C Bump circuit" It takes a input from the compressor and mixes it with ECM's fan controls to mix in fan control with the A/C being on. If the fans are on low and A/C is turned on the fans go to high, If the fans are off and A/C is turned on the fans go to low.. Etc.

https://www.pcmofnc.com/product/hot-...-bump-circuit/

Alvin!!! Turns out the truck DOES have a pressure sensor so you are right! All I did was copy the fan AC pressure settings from a tune file from a buddies 06 Silverado with factory fans and voila! I always love a simple fix. Thanks for pointing me in the right direction!

That bump circuit does look like a good solution for those who don't have a pressure sensor already.

This is doubly good news as I just recently begrudgingly replaced the fan clutch on another truck of mine, an 03 2500HD. I checked that truck and it has this same sensor, so, it must be possible on that one as well. That truck will eventually get a Taurus fan as well now that I know I can make the fan come on with the A/C.

Thanks again.

Now maybe if I want to further refine my electric fan conversions, I could add the low speed functionality. I've just been running them on high speed only.


This must be the pressure sensor I suppose? It's on one of the lines coming off of the compressor: