Controlling rad fans with A/C

Winkernod

Winkernod

Greasemonkey
Sep 13, 2018
131
43
London Ontario
Just finishing up getting all of the A/C components pulled together and installed on my LS but was wondering what others have done for the rad fan control when the A/C is running. I am running the original truck ECM and have the ECM controlling the dual fans at two different temps. My question is : Is there a pin on the ECM I can tie into that will turn the fan on while the compressor is engaged or is there a better way other than just using another relay feeding directly from the compressor to the fan relay
 
O

ostrich

Greasemonkey
Aug 27, 2012
149
43
Ontario, Canada
I'm going to be doing the same soon. Not sure if you are using the PCM to turn the fans on for cooling? If so, I'm pretty sure when there is an AC request the PCM will turn the fans on automatically. I haven't dug too deep in the schematics yet, but I was hoping to have mine work like that. One difference is I'll be flashing my truck PCM with a Camaro OS. They have 2 electric fans.
On another note I have a 2004 F150 that I put electric fans in. I wired a relay off the compressor wire. Drawback every time the compressor ran the fans did.
 
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Winkernod

Winkernod

Greasemonkey
Sep 13, 2018
131
43
London Ontario
Okay I am using the ECM (PCM)to control the rad fans however I am not using ECM to control the A/C system as it would have from the donor vehicle. I did find in the pin out list from LT1swap.com the blue connector pin #42 might be the answer.
 
O

ostrich

Greasemonkey
Aug 27, 2012
149
43
Ontario, Canada
Looked it up. Looks like it's a Fan1 relay input, just not sure how the PCM controls it and when?
 
Winkernod

Winkernod

Greasemonkey
Sep 13, 2018
131
43
London Ontario
Yeah i'm not sure either but I think that is what I want, when the A/C compressor is engaged then so will the fan be. you want air over condenser to cool it even if your not moving
 
O

ostrich

Greasemonkey
Aug 27, 2012
149
43
Ontario, Canada
I looked into Pin#42 from my Camaro schematics and it is the same Fan#1 control as a truck 411 PCM, so it should work.
The PCM will complete the ground path for cooling fan relay #1 under any of the following conditions:

• When engine coolant temperature exceeds 105°C (221°F).
• When A/C is requested and ambient temperature is greater than 10°C (50°F).
• When A/C refrigerant pressure is greater than 190 psi (2 volts).
 
Winkernod

Winkernod

Greasemonkey
Sep 13, 2018
131
43
London Ontario
I looked into Pin#42 from my Camaro schematics and it is the same Fan#1 control as a truck 411 PCM, so it should work.
The PCM will complete the ground path for cooling fan relay #1 under any of the following conditions:

• When engine coolant temperature exceeds 105°C (221°F).
• When A/C is requested and ambient temperature is greater than 10°C (50°F).
• When A/C refrigerant pressure is greater than 190 psi (2 volts).

Ostrich That is exactly what I was looking for Thank you for the info. That really helps me.
 
J

Jimmy girl

Not-quite-so-new-guy
Oct 11, 2014
45
18
What Ac are you using ? I’m using a sanden sd7 compresser connected to the factory Ac box . When my ac turns on , the fans go on high . I bought a PWM fan controller from painless . Controls dual fans . Soft starts them and they go up and down according to temp . Nice thing about it is my car doesn’t sound like an airplane .
 
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Winkernod

Winkernod

Greasemonkey
Sep 13, 2018
131
43
London Ontario
What Ac are you using ? I’m using a sanden sd7 compresser connected to the factory Ac box . When my ac turns on , the fans go on high . I bought a PWM fan controller from painless . Controls dual fans . Soft starts them and they go up and down according to temp . Nice thing about it is my car doesn’t sound like an airplane .
I am also running a Sanden compressor on the factory A/C box. I have the electric fans controlled by the PCM and just wanted to make a neat connection of the two. and this sounds like that this will do that. a single wire from the A/C compressor into the PCM. I have dual fan setup out of an Intrepid with the PCM controlling the the fans at different temps
 
Winkernod

Winkernod

Greasemonkey
Sep 13, 2018
131
43
London Ontario
Looking closer at pin 42 I don't think it is one I want to tie into. I was looking for a trigger wire that I could apply 12v to and it would then turn the fan on but pin 42 is actually the ground to complete the circuit to run the fan. So I believe that I will need to add another relay.
 

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